This myth, and "cant yell fire" are two of the most pervasive false legal statements on the internet.
"Quite simply, the view that a trademark holder must trawl the internet and respond to every unauthorized use (or even every infringing use) is a myth. It’s great for lawyers, but irritating and expensive for everyone else. And when done clumsily or maliciously, it chills free expression."
-- https://www.eff.org/deeplinks/2013/11/trademark-law-does-not...