You can purchase a plain vest here:
http://www.sitstay.com/store/clothing/service1.shtml
If you scroll down, you will see they have a patch you can sew on the vest which says "I'm friendly - ask to pet me".
IMHO, If your dog is well trained and socialized, there is no reason why you can't walk him around people without a muzzle. Your responsibility is to have your dog under control and if you do, there's no reason why you shouldn't be there. If some people want to cross the street or give you looks, then that's their problem.
If you want to give your dog lots of friendly contact with people, why not train him as a therapy dog, get him evaluated and registered with Delta Society, TDI, or a local group, and visit a nursing home once a week? Your dog would probably love it, and you would be doing a great service for the residents of the home.