Many car dealerships use local shops for secondary signage. If the secondary signs display the exact same logo design as the main sign, the secondary sign would no more be a trademark infringement than the main sign. Trademark law does not specifically prohibit copying a mark. It forbids creating confusion among consumers as to the source of goods. If a GMC dealership displays secondary signs with the GMC mark, what confusion is caused?
It's true that copyright law prohibits copying without permission. But the GMC logo, consisting of three stylized letters, does not qualify for copyright protection. Copyright is not at issue.
However, what if the dealership is required to use only certain suppliers but they don't tell you this? If they violate an internal GMC policy, then they should not even be ordering signs from you in the first place. It's not an intellectual property issue. It's a policy issue. Make sure you have a legitimate purchase order from them and get your money. Let the PO include details, such as that the "logo will be created to comply with GMC branding guidelines." Of course, get a copy of the branding guidelines from the car goober, or ask for his corporate contact so YOU can request guidelines to save him the trouble. Tell him that you will make sure that he does not get in trouble with his corporate overlords.
A logo sign that does not comply with branding guidelines may not be considered infringement, but it could be considered trademark dilution, which is part of trademark law. Somebody in authority needs to sign off on the proofs for the job.
If an authorized dealership refuses to give you branding guidelines, or will not let you request them, that is suspicious. It's not that you will go to prison for duplicating a GMC logo for a GMC dealer—that's absurd—but you could be stiffed for the money.
Brad in Kansas City