You can buy good quality rubber double-sided sticky tape - the kinda stuff used to stick on car badges and trim and the like. Its sticks to the preverbial blanket. The secret of getting any adhesive to stick to car bodywork is to use a silicon cleaning solution first. If there is the sligtest trace of silicon nothing will stick for long and that includes paint.
I am sure you are not the only one to have a number plate fall off Delta,even Lagtdi has suffered the same on his lovely Lancia.
(Could happen to anyone).
Yep,my front one fell off but I managed to find it and reattach it with some screws,the rear one fell off without me knowing it until a friendly biker pulled along side me and told me that 'you've got no rear number plate mate!'.
The sticky pads do work,but only on certain materials.I tried to stick my plates on to the dimpled plastic behind them and it didn't work,but if the area is clean and flat (and even better,it's a warm day or you heat the area with a hair dryer/hot airgun) they stick like sh1t to a blanket.
I'd rather push my Alfa than drive a BMW....
Currently in Lagdti's garage: 2004 Saab 9-5 HOT Aero and a 2001 Audi A3 1.8 Turbo