Nah, I don't see what the harm is if its to your own site or a site you like. If it's something obvious, though... Like if this was your sig:
WANT YOUR OWN PROFESSIONAL WEBSITE THAT WILL BRING YOU LOTS OF CASH $$$$$$$$$ ??!!! I DO WEB DESIGN! BEST RATES YOU'LL FIND! MAKE LOTS OF MONEY IN JUST A FEW WEEKS WITH A UNIQUE WEBSITE!!! GO TO MY WEBSITE NOW AND SEE FOR YOURSELF!
Now that would be annoying.