Wouldn't it be better to have a board for the promotions though? That way more people would see them. If we just post in some other board then nobody will even see them. So many people are posting in all of these boards every 5 minutes so it will just get buried and become unnoticed.
People can do as you have done where you have used your site as a signature line and under the avatar. If anyone is interested they can always PM the poster and ask about the site. Have you gotten any/many inquiries about yours ?
As for special boards … people seem to tend to just stick to one or two or at most a few familiar places and don't wander around very much SO a new boards would most likely be lost anyway.