What is a decal used for in the context of vehicle inspections?

In the context of vehicle inspections, a decal serves as an important identifier that verifies that a vehicle has passed inspection requirements. Specifically, the gummed decal attached to a motorcycle indicates that it has met all necessary safety and regulatory standards. This decal is a form of proof for both law enforcement and the vehicle owner that the motorcycle is in compliance with the laws governing inspections, ensuring that it is safe to operate on public roads.

The other options do not correctly capture the primary purpose of a decal in relation to vehicle inspections. For instance, while a sticker indicating ownership history might provide useful information, it does not relate to the inspection status of the vehicle. A label for vehicle mileage is more about tracking the vehicle’s performance and history rather than its inspection compliance. Additionally, using a vehicle for advertising purposes does not pertain to inspection or safety regulations and therefore does not align with the function of an inspection decal.