However an anonymous person could not do anything about enforcing their copyright without losing their anonymity. You can't sue someone anonymously (you as the plaintiff), you can't DCMA anonymously, etc etc.

Trademark is a registration mark unlike copyright (copyright is automatic in almost every state in the world according to a few treaties). Broadly, provided you pay your fees then you retain a granted trademark. There are trademarks that are unregistered, acquired by use in trade, but it's a very weak instrument. Non-use can be grounds to contest a trademark - so it's almost impossible to retain a mark and remain anonymous as you need to be trading using that mark and usually trading requires you to disclose identifying information in some way.

Also USPTO's TESS facility gives the trademark assignee information, http://assignments.uspto.gov/assignments/q?db=tm&qt=sno&reel... .