touching belly

so has anyone else had people already start to touch their belly. I'm almost 13 weeks and I already have had some closer friends rub my belly. I really feel uncomfortable with it. I didn't say anything but why do people think oh your pregnant, I need to touch the belly.

Now what's a polite way to tell people not to, without sounding rude. the only person I want to touch my belly is my husband. not my mother or mother in law. but what's a way to tell people without sounding rude.