What tool is required for validating inspection stickers and decals at an inspection station?

The punch is essential for validating inspection stickers and decals at an inspection station because it is specifically designed to create a unique pattern or mark on the sticker. This process effectively certifies that the inspection has been completed and confirms that the vehicle complies with regulatory requirements. Using a punch helps to prevent the sticker from being reused or illegally transferred to another vehicle, thus ensuring the integrity of the inspection process.

Other tools mentioned, such as a window tint meter, are used for measuring the light transmittance through a vehicle's windows, while a tire tread depth gauge is meant for assessing the remaining tread on tires. String and nut, on the other hand, are not relevant tools for vehicle inspections. Thus, the punch serves a unique and vital purpose in the inspection process, making it the correct choice for validating inspection stickers and decals.