A further suggestion, if traffic is going up and down like a yoyo, is to keep the content fresh, as well as keep posting regularly on other forums, which allows advertising in signatures. If you are gonna advertise in signatures on other forums, like others said, I would strongly suggest to have a catchy signature which will catch a readers attention. For example, if a forum board is something about shirts, their design and so forth, a signature could be colourful with a small shirt and maybe a phrase or line after the URL (in the signature of cause) leading the reader to the site.