They can surely tell if they want to. It used to be their stated policy that they do not try unless requested by law enforcement. I don't know if that policy is

They can surely tell if they want to. It used to be their stated policy that they do not try unless requested by law enforcement. I don't know if that policy is still in place. This is in complete contrast to FB, whose modus of operandi had always been "we will do whatever we can to figure out who you are".