From the late 60's to the late 80's, motorcycles were issued inspection stickers that went either on the outside of the windshield, or on the bike itself.
The adhesive was on the back of the sticker so it could be placed anywhere.

Starting in 1992, the inspection stickers for motorcycles went on the license plates.

In 2003, when the inspection period for new cars was changed to 4 years, new motorcycles started receiving distinct "New Motorcycle" inspection stickers starting with 2007 expirations.

As of August 1, 2010, New Jersey no longer requires inspection stickers or registration stickers on motorcycle plates.