I still have a personal space!

It's very interesting to me how so many people think that pregnant women do not have a personal space anymore. Let me explain my statement.
I have noticed that over the past few months, ever since my belly became to resemble a basketball, people have this desire to touch my belly all the time. And I do not mean my friends, I mean random people, the ones that you say "good morning" to at work, but don't exchange any other words at all, or even complete stranger who you have just met.
The other day, this woman whom I have seen in the office but have never talked to, came up to me and said "oh, you are pregnant" and proceeded in rubbing my belly! I can not even tell you how disturbing that is! I mean, I am ok with friends touching my belly, especially if they ask before, but complete strangers?

My husband A mentioned a while ago when I first complained about this that next time when it happens I should touch their bellies as well. And guess what, my resolution after the last uncomfortable encounter is that I am going to do so! I am just not sure how I could tell people that being pregnant does not equal with no personal space or a sign that says "please touch and rub my belly"!