I think since it's your signature you can advertise yourself in any way you please...well, okay, unless it's explicit, but I'm assuming it's not in this case. I think you can plug whatever you want, as long as it's not distracting/explicit/spammy...basically, follow the normal rules. The only other thing, is that they prefer it not take up tons of space; just us a spoiler tag to get around that.
Hope I've helped; and if I happen to be wrong, someone's free to correct me.