It's a good question. I would suggest always just asking the Admin first if it's ok to post a message promoting your board, and then abiding by the Admin's answer. If they say it's fine, then go for it!
I'm actually the Admin of a totally unrelated forum to YorkieTalk, (it's a DVD review site) and since I like YorkieTalk, I encouraged Fasteddie to post a quick note about his board on my site.
In fact, if you Admins hit it off then maybe the two of you can swap ideas, user notices, banners, etc. and it becomes more of a community thing as opposed to just a somewhat anonymous plug. This way, it's just good karma all around.
