Normally I wont let strangers touch my kids. Unless they are from their pre school, people that I have seen in church.. those I have never seen before I will carry my baby away as fast as possible. For those from church or other parents, normally after event ..I will wipe my baby's hands or wash.
Oh my, that's one thing I dislike too! People loves touching my baby's hands too. I usually tell them that my baby loves to put her hands in her mouth and her hands wet and sticky from her saliva, I don't want your hands to get wet from her saliva. Smile and quickly walk away :)
I tell them to stop. It's ok if I sound rude but they are strangers after all. Our baby's health is ultimately more important than hurting some random stranger's feelings
offer him or her to wash hand.