What forums do you post in that allow a sneaky link?

[YooHee]

How does Google know if a site's webmaster has been banned from a forum?

i think it will depend on the webmaster now..... if he or will allow the banned member's signatures on the forum....

[RiverWire]

Well go and post links into your post but make sure that you dont spam the board and the link you are posting is relevant to the topic..
Remember one thing.. if you get banned from many high PR forums and site then google will penalize your site for which you are posting links and your effort will just be a waste...

If you are banned the google wont know, many people on the internet still have a dynamic ip address so there would be no real way of keeping track , it would also be easier for you competitors to get you banned.

Most forums remove signatures for banned members.