A majority of my cars have been custom factory ordered vehicles. The last thing before signing the order, I always ask that no dealer decal be applied to my car. Dealers have always did as asked. On my C, that I ordered two weeks ago, the salesman said that he personally would take it off, if the service people do it before he sees it. I will insist that they do take it off, if it is there. If a dealer gave me a problem, I would tell them to take $500-1000 off the price of the car. My advertising fee.
When a dealer puts a license plate holder on the back with their name boldly visible. It is no problem. I just take it off when I get back home. I have plain black license holders, which have a clear plastic license plate cover, and is held in place with security bolts (allan wrench headed bolts).
I think it extremely bad taste to put dealer decals on premium or near-premium cars. I have never gone to a dealer because of a dealer decal, on a car trunk. Makes no difference to me. I go to the dealer that I like their sales & service practices. There is a dealer that is less than five miles from me that I will never complete a deal. I use them just for test drives and oil changes. Other area dealers have a low opinion of this locally well known dealer.
I make referals or recommendations to good dealers. They need not put an ugly decal on my car.