It was commonplace in the 70s & 80s for the factory to put Buick decals on the engines air cleaners. Not so much today.
Other spots on the cars that would get decals are underhood for belt locations, A/C specs, engine details, etc.
G bodies received an alarm sticker, politely telling would be thieves to stay away (but also revealing to the smart ones exactly what they needed to know to disable since most factory alarms are setup the same way!)
There were also Buick decals created for the dealerships that sold the Buick model line of vehicles.