You're right, noone has to follow the links... but what purpose is a link used as a sig, other than to follow it? Well, I guess it was meant as plain provocation. And I fall easily for that.
I found this nice place about adventure gaming, the kind of games I like most, then someone has me clicking on his sig, and - shazam! - I'm confronted with religious zealotism and pro-war-propaganda.
Quite unfunny, being confronted in here with the same s**t as in every other, bigger, longer existing forum. It just took a day or two to drag some evil 'reality' in here...
On the other hand, I clicked on another users profile and was delighted about his great MM fanpage: http://members.fortunecity.com/harang/
You're also right about the off-topic URL posting in general - I'm gonna lose my sig about Ubuntu-Linux...
Sorry about the harsh words,