I normally tell them to not add any decals (as they add them when they sell the vehicle to the customer vs. dealer swap) Along the same lines.. nothing else goes on my bumper. (includes my views either political or spiritual) my car and yard* is like this forum post no bills.

*including why would you let a potential thief know you have ADT or another alarm? let them kick the door in and it does it's job. Don't let them know the type so it can be defeated. - I get it they will see the sign and move to a non sign home. just my leave the car/yard clear theory.