Thought of the same thing greentea. I guess he got inspired by heero.
eU61, earlier u said c shaped is crescent and d is decrescent, now you've reversed it?
As for explaining to ur children , it's like this, the word 'ambulance' is written in mirror image on the front so that the vehicle in front reads it as ambulance in the rearview mirror, same for crescent/decresent.