[BillyCoxDodgers3B]

Very early on, Mays would sometimes print the "s" in Mays separately from the rest of his last name and tended to space it too far away from the rest. One of his million signature charateristics. Whoever was responsible for the facsimile likely missed the s when they traced over the signature they used for the purpose.

Most of the time, the "s" more closely resembled an s. The one illustarated below looks like a "c", or maybe even an indiscriminate pen mark. Therein you've likely found your answer as to why "Willie May" lives on in perpetuity.