Are you naive or what? every time you post something your computer IP should appears on their screen.
The problem is when several people use the same computer to access the forum it's hard to know who posts what.
We are four people using the same computer. Some like politics, some like tabloid-related issues, some are on the left or the right.
But my uncle hates it every time he sees we use his work computer to chat in discussion forums. He says it's a waste of time that should be rather spent to study.