Depends on how much $ we're talking about for one. If the price is right, I certainly would... as long as it's something I wouldn't feel like a homo representing.
Also... Jon, I'm very surprised you'd be ok with that. I can't think of a single other forum that would allow it's user's to place banner ad's in their sigs that they're being paid for. It would seem to be even less allowed in this industry. That's really cool of you to be so 'lax about the moderation of the forums.