Patent marking is optional in the same way that keeping receipts is optional. You can skip it, and it costs you at exactly the moment it matters.
The rule is in 35 U.S.C. 287. A patent holder who makes or sells a patented article and does not mark it generally cannot recover damages for infringement occurring before actual notice was given.
Which converts a formality into money. An unmarked patent holder who discovers three years of infringement may recover from the date they sent a letter, not from when the infringement started.
And the reverse rule bites too. Marking a product with a patent that has expired or does not cover it is false marking under §292.
What marking buys
| Marked | Unmarked | |
|---|---|---|
| Constructive notice to the world | Yes | No |
| Damages from | The infringement start | Actual notice only |
| Effort required | Ongoing | None |
| Risk if done wrong | False marking | — |
Constructive notice is the whole point. Marking puts the world on notice, which means an infringer cannot say they had no way to know.
Without it, the damages clock starts when you tell them. In practice that is frequently the date the complaint was filed.
Who must mark
| Party | Must mark to preserve damages |
|---|---|
| Patent holder making the product | Yes |
| Licensees making the product | Yes — their failure can limit your damages |
| Distributors | Should, if selling the article |
| A holder who makes nothing | No article to mark |
| An NPE with no products | Nothing to mark |
Licensee non-compliance is the trap. The statute looks at whether patented articles were marked, not at who made them, so a licensee shipping unmarked product can limit the licensor's recovery against a third party.
Licence agreements should require marking and give the licensor a right to verify it. That clause is cheap at signature and unobtainable afterwards. See patent license agreement.
Method claims are different
| Patent contains | Marking required? |
|---|---|
| Only method claims | No — nothing to mark |
| Only apparatus claims | Yes, if articles are made or sold |
| Both, and articles are sold | Yes, generally |
| Both, and only the method is practised | More complex |
Method-only patents escape the requirement because there is no article. That is a genuine advantage for damages purposes and it occasionally influences claim drafting.
Mixed patents are the difficult case. Where a patent has both and the holder sells articles, courts have generally required marking to preserve damages on the apparatus claims.
How to mark
| Element | Detail |
|---|---|
| Word | "Patent" or "Pat." |
| Number | The specific patent number, or a URL for virtual marking |
| Location | On the article where practicable |
| Alternative | On the packaging, where marking the article is not practicable |
| Multiple patents | List all that cover the article |
| Format | Legible and durable |
Marking the article beats marking the packaging. Packaging is discarded; the article persists, and it is what an accused infringer examines.
Only list patents that actually cover the article. Listing a patent that does not is the classic false marking scenario.
Virtual marking
Permitted since the America Invents Act in 2011, and now the standard approach.
| Physical marking | Virtual marking | |
|---|---|---|
| What appears on the product | Patent numbers | "Patent" plus a URL |
| Updating when a patent issues | Retooling or reprinting | Edit a page |
| Updating when a patent lapses | Often impossible | Edit a page |
| Risk of stale information | High | Low, if maintained |
| Cost to maintain | High | Low |
The page must be freely accessible and must associate products with patents. A list of patents with no indication of which products they cover does not do the job.
The maintenance obligation is real. A virtual marking page listing patents that expired two years ago is the modern form of false marking exposure, and it is entirely avoidable.
Quarterly review is a reasonable default, plus an update at every issuance, lapse or product discontinuation.
False marking
| Element | Required |
|---|---|
| Marking an unpatented article as patented | Or an expired or inapplicable patent |
| Intent to deceive the public | Yes — the key element |
| For a private claim | Competitive injury |
| For a government action | Civil penalty |
Intent to deceive is what saves most honest mistakes. A number left on packaging after expiry, without more, is generally not enough on its own.
The America Invents Act narrowed private claims substantially. Before 2011, anyone could bring a qui tam action; now a private plaintiff must show competitive injury, which ended the marking-troll litigation wave.
Expired patents get a safe harbour. Marking with a patent that covered the article but has since expired is expressly not a violation, which removes the biggest practical worry.
The lapse problem
Most utility patents do not reach full term.
| Ipiry Patent Survival Curve v1.0 | Rate |
|---|---|
| Survive the 3.5-year fee (2022 cohort) | 85.8% |
| Survive the 7.5-year fee (2018 cohort) | 64.6% |
| Reach full term (2014 cohort) | 41.4% |
| Abandoned before full term | 58.6% |
Computed from 27,273,654 USPTO maintenance fee records covering 8,262,336 US utility patents — see the patent survival curve.
Which means marking goes stale constantly. A product marked with four patent numbers in 2018 may be marked with two live ones and two dead ones by 2026, and nothing prompts the update.
Virtual marking solves this and physical marking does not. Moulded numbers outlive the patents they name by years.
Worked example: what unmarked cost
A company discovers a competitor has been infringing for three years.
| Marked | Unmarked | |
|---|---|---|
| Infringement began | Month 0 | Month 0 |
| Discovered | Month 36 | Month 36 |
| Demand letter sent | Month 37 | Month 37 |
| Damages recoverable from | Month 0 | Month 37 |
| Infringing units in the period | 180,000 | 180,000 |
| Units within the damages window | 180,000 | ~5,000 |
| Reasonable royalty at $4/unit | $720,000 | $20,000 |
The same infringement, the same patent, the same royalty rate. The difference is whether the product carried a marking.
Adding a URL to the packaging would have cost almost nothing and preserved $700,000 of exposure. That arithmetic is the entire case for marking.
When marking does not apply
| Situation | Marking requirement |
|---|---|
| Patent holder sells nothing | None — no article |
| Method-only patent | None |
| Licensee sells, holder does not | Licensee should mark |
| Software delivered electronically | Fact-specific; splash screen or documentation |
| Component inside a larger product | Mark the component where practicable |
Software is the awkward case. Where there is no physical article, marking is usually done in documentation, an about screen or an accompanying notice, and the position is less settled than for physical goods.
Marking on acquisition
A patent bought from someone else carries the previous owner's marking history.
| Check at acquisition | Why |
|---|---|
| Did the seller mark? | Affects recoverable damages for past infringement |
| Did licensees mark? | Same |
| Are accrued causes of action assigned? | They do not transfer automatically |
| Is a virtual marking page current? | It becomes your problem |
Accrued causes of action must be expressly assigned. The right to recover for past infringement stays with the previous owner unless the assignment says otherwise. See patent assignment.
A seller who never marked has limited past damages to give you, which affects what the patent is worth.
Marking multiple patents and products
A product line covered by several patents needs a system, not a decision each time.
| Situation | Approach |
|---|---|
| One product, several patents | List all applicable numbers |
| Several products, overlapping patents | Virtual marking page with a product table |
| A patent covering only one component | Mark the component where practicable |
| Patents issuing over time | Page updated at each issuance |
| Patents lapsing over time | Page updated at each lapse |
A product table is what makes virtual marking work. Listing every patent the company owns, without saying which covers what, does not give constructive notice for any particular product.
Build the update into the patent calendar. The same review that decides maintenance fee payments should trigger a marking page check, since both turn on which patents are live.
Patent marking: the checklist
- Mark if you make or sell a patented article. It is optional and it is worth money.
- Use virtual marking. A URL is trivial to update; moulded numbers are not.
- Associate products with patents on the page, not just a list of numbers.
- Mark the article where practicable, and the packaging only where it is not.
- Require marking in every licence, with a right to verify compliance.
- Review the marking page quarterly, and at every issuance, lapse or product change.
- Remove patents that do not cover the article. Listing inapplicable patents is the false marking risk.
- Remember method-only patents need no marking, and note it when drafting.
- Check marking history when acquiring a patent, since it caps past damages.
- Expressly assign accrued causes of action on any purchase, or the past infringement claim stays with the seller.