SevenCubed - 4:27 pm on Sep 17, 2012 (gmt 0)
These days it appears to be walking on thin ice at least from google's perspective. Maybe less so if the forum is related to your niche as RegDCP points out.
It's probably too late for you because you have your domain up and running already? This is where pre-planning domain names is very practical. When possible I will try to encourage a new business-owner-to-be to select a business name that includes an obscure descriptive word that is in such a grey area that it can almost be considered as a noun, adjective, verb, etc... so that when participating in forums offsite they can squeeze that word into the discussion in close proximity to the keywords being discussed and as long as it's relevant it's pointing to their domain in a round-about kind of way without the need for a signature.