Why You Should Use the NoticeUsing the notice does inform others that the patenting process has begun, which may make them liable if they infringe upon your intellectual property. However, you should remember that the application by itself does not confer any legal protection. You will only be able to challenge patent infringements if the patent is actually issued. As such, the notice is purely informational until the process is completed. It then is recognized as due warning that the invention is protected, making anyone infringing upon it liable. (To benefit from patent protection, other parties must be informed that your invention is patented.)
When You Can Actually Use the NoticeThe fact that the "patent applied for" notice doesn't confer any protection until the patent is granted doesn't mean it can be used freely. Under U.S. law, you can only use patent application notices once you have filed an application and it has been accepted for examination. Using the notices when no patent application has been filed is expressly prohibited. The penalty for using the notices in such a way is considered false marking and punishable by a fine of up to $500 per offense. Each offense is counted separately, and the fines can quickly become overwhelming in the case of high-volume goods.
If you have a question about the patent process, ask a lawyer.
This article contains general legal information and does not contain legal advice. Rocket Lawyer is not a law firm or a substitute for an attorney or law firm. The law is complex and changes often. For legal advice, please ask a lawyer.