Bladewire - the point of TMing the watermark is so you don't have to prove who uploaded the content. There's no free pass for "anonymous" uploaders. If the stripped content is sitting on their servers and they have notice (in the Ninth Circuit) it can lead to a finding of contributory TM infringement...
Here's what I wrote about it 3 years ago...
Piracy and Trademark Law: A Way Stop to Content Theft - AdultBizLaw
And here's a quote from a legal treaty on TM infringement...
?Liability for trademark infringement and unfair competition may be extended beyond those who actually sell goods with the infringing mark, to include those contributory infringers who knowingly cooperate in illegal and tortious activity.? J. Thomas McCarthy, McCarthy On Trademark and Unfair Competition (2002) §§ 25:17, 18, referencing Warner & Co. v. Eli Lilly & Co., 265 U.S. 526 (1924) (applying common law concept of contributory infringement).
And here's the Ninth Circuit case that extend liability to the hosting companies...
http://cdn.ca9.uscourts.gov/datastor...2/10-15909.pdf