What is the difference between a Sunni and a Shiite Mosque?

I am considering converting to Islam at a mosque in my area. I have never been to a mosque before, so this will be my first time. I'm not sure what type of mosque this mosque is I am not sure wether it is a Sunni mosque or Shiite, and I don't want to be rude by going right up to someone and asking. So what is the best way to tell?