You can make your own stickers. Go to a office supply place and by a pkg of stick on labels. Take a digital picture of any French seatbelt/airbag from any car or truck and in your windows program there is usually a publisher program. Add the picture of the sticker from the car/truck digital and tell your printer how big the labels are, then print your labels.
Or go to a auto wreckers and pull some off the visors of car going to the shreader.
I don't know for sure, but you probably could get away with hand printing them too.
Print one with this on it "Portez votre ceinture de sécurité ou vous mourrez" and stick it on your visor. If the guy doing the inspection speaks French you should pass.