The chips were bought in 1938 before it was the Paddock.
Per the Mason record card, the S should stand for "Sinclair" as in Sinclair Grill.

Mr Tobin could very well have taken the chips with him when he sold the Sinclair.

"(I know we Northern Kentucky guys will find some match to any letter on a chip)"

True but those Texas boys are just as bad if not worse.