Using forum signatures as a part of the linkbuilding can be little bit questionable/risky practice.
Why? Because Google treat this as an attempt to manipulate website ranking and thus it may penalize such website linked from signatures.
Here is the explanation from Google itself regarding forum signature linkbuilding: https://support.google.com/webmasters/answer/66356?hl=en
search word "signature" on that page
Note that tophostingforum has nofollow attribute to the signature links so it should be safe to use links in signatures
In my oppinion signatures are way to advertise.