Dave, I am sure some one has emailed you already, but just in case no one else has responded, here it is: any chip that bears the denomination of $2.50 is a snapper....As for the meaning it was as far as I know; dubbed "snapper" because it quickened or snapped up the ability for the dealer to pay off $5 bets whenever, a blackjack ocurred.
Hope some of the old timers will respond if this isn't correct. Reggie