From the late 60's to the late 80's, motorcycles were issued inspection stickers that either got placed on the windshield, or on the bike itself.
1973/74 cycle sticker in use on a motorcycle fender
Starting in 1992, the inspection stickers for motorcycles went on the 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.