Very nice gift. What you have received is a Silver Indy 500 Pit Badge. The number at the top is just a numeric count and doesn't mean anything other than the order they were issued in. They were issued to VIPs, drivers,pit crew members,sponsors, police, emergency crews, car owners, prize providers, judges, ticket sellers, media people and members of the press, messengers, captains, and maintanance people. They allowed the holder to gain access to the pits and garage areas every day of the 500 festivities (including race day with a backup card that was issued on race day morning to silver badge holders).
There are also bronze pit badges which have a letter and 1-3 numbers at the top. They were available for purchase by the general public and allowed the same entrance except not on race day.
Hope this helps you with what you have.
[This message has been edited by GTMN (edited 07-14-2009).]