The traditional 'classic' Adidas sneaker design features a heel tab / patch; shown below in a range of configurations.
The heel tab dates back to the 1950's, Adidas were founded in 1949 and the heel tab was already a feature of early Adidas shoes; like the Adidas Samba. The early heel tabs were plain (shown far right, above) because Adidas did not create a logo until 1971. Adidas became the victim of counterfeit shoes in the late 1960's, and to combat these shoes, Adidas produced a trademarked logo: the Trefoil logo, shown above left. The design of these heel tabs, while not being identical, have a similarity. Virtually every heritage Adidas shoe features a heel tab, but modern Adidas shoes do not feature a heel tab to the same regularity - the Trefoil logo has been discontinued and is only used on heritage products.