Plugging a forum in
another forum is a serious no-no on most sites. It's considered very bad manners and some webmasters/administrators don't allow it because they think that advertising another forum in their forum is stealing members from
their site.
Personally I don't take one-time plugs for another forum too seriously. I do however consider putting a link to another forum in your signature as extreemly rude. Another website, like your personal homepage or something is okay, but another forum is very bad netiquette.
So to make a long story short:
One time post to inform others of another forum that could be interesting is okay.
Posting more than once or even worse: linking another forum into your sig - is
not okay.
Thanks for posting and asking! That's very good.

I hope you will now remove that link from your sig Sven.