This comes right off of Dan Wickett's Token Website (Dan is a great guy and I respect his information) It is my understanding he pulled this right out the Franklin Mint Catalogs from 1968 - 1970 (I don't know which year).

"In 1967, the Franklin Mint introduced gaming tokens in three additional denominations - $5, $2 and 50 cents. The quantities of gaming tokens minted for casinos in 1967 ranged from a low of 500 to a high of 100,000. In addition to those pieces minted for actual use in the casinos, 1,550 Proof-Like sets and 500 Proof sets were also minted. This year for the first time, all specimens (regular, proof-like, and proof) of the same token were struck in the same material, the only difference being the surface finish. An exception occurred with the last nine $5 specimens for collectors were struck in Bonded Silverclad for the casinos but the Proof and Proof-Like specimens for collectors were struck in solid Sterling Silver. The Sterling pieces can be readily distinguished by the word STERLING included in the design on the obverse."

If you look at the T-Bird Token it has no STERLING under the Hotel.

I have seen the T-Bird, Harold’s Club, Caesars Palace, in Silver Clad.

CT take a look at my example of both types of T-Bird Tokens. The one on the left is David's Silver Clad the one on the right is a Sterling one.