List some situations where the letters on signs are reversed. Explain why it is being done.?

Answer 1

The only one I can think of is that the front of an Ambulance has it printed in reverse, so that it appears normal in your rear view mirror.

Answer 2

Rental trucks and semi-trailers have the height of the box printed on the front of the box where it can be seen in the rear view mirror to remind drivers of the height.
Some companies name their company or give their logo across the hood in reverse - this lets drivers they are following read it in their mirrors and attracts the eye of people looking at it because it confuses the brain doing instant recognition and thus they study it or read the side of the vehicle.