Ummmm....think a sleeping policeman is actually a little different from a thank-you-ma'am. There's a discussion about this on another thread (can't remember the name of it, sorry!) - about the difference between these two things and potholes. (Maybe do a search on "pothole" if you're interested.)

A thank-you-ma'am is not put in the road to "calm traffic" as a sleeping policeman is; nor is it quite a pothole. It's an unidentified ridge in the road.

I was on a tour bus in outback Oz when we went over a BIIIIG thank-you-ma'am. None of us tourists merely nodded as we went over it - we were all flung into the air and someone at the back of the bus actually landed on the floor and wound up with a serious bruise as a result, and someone else told me she thought I was going to go through the windscreen (I was riding shotgun at the time). I had not been wearing a seatbelt because the driver used to make fun of me when I reached for it. After that, I ignored the peer pressure and buckled up every time....!