I signed no such thing myself..
I do believe that by clicking ' I accept the terms and conditions' box, which you HAVE to do to open an account, is the same as putting down a sig. Everywhere has it's rules, and every site has an ethic they would like to promote. Up to us to choose whether we dig it or not, which should be the key factor in determining our stay and level of activity. You can push the boundaries a little bit on threads where you and a bunch of fellas have been hanging out for a long time and get away with a bit of sillyness, but if a mod pops over and draws the line then consider the party over and calm down a tad.
It is like this on community forums everywhere. Sure freedom of speech exists and all of that. But so does the freedom to not listen, and the freedom to enforce the rules of your organisation too. There is no absolute freedom on the internet or anywhere else.