Usually there is an @author tag in API documentation (JavaDoc, PHPDoc etc). Is it acceptable to use this tag on every function you make in a commercial product? 
Specifying Author in Source Code in a Commercial Product
documentation;tagging
The author tag may serve two purposes:Claim code ownershipProvide a point-of-contact for future code maintenance needsPurpose 1 may be a legitimate use for some projects, but its use must be governed and enforced by the project team. For commercial closed-source project, it is likely that this usage could be forbidden.Purpose 2 may serve a legitimate, yet transient (temporary) need to help establish multiple points-of-contact in distributed teams that don't normally communicate. In other words, teams that had broken or non-existent communication channels, and missing some standard software development practices. Putting that information in a project wiki, or ensuring that source control commit history is accurate and accessible to everyone (developers as well as API users), will be a better alternative.Consult with project lead if you encounter this tag in existing code, to see whether it should be kept or removed.If you see this tag that refers to a person not in your company, it may be a sign of improper code appropriation (e.g. stealing code from other sources without attribution and/or licensing), which is a different and much bigger issue.