This is a very early ashtray from Harrah's in Reno. It is a fairly rare tray but Mark shows seven different versions of them on his Nevada Casino Ash Tray Project site:

http://www.nevadacasinoashtrays.org/

Go to that site and you can see the early history that covers the time frame that these were most likely used. In 20 years of searching I have only manged to find one of these out in the wild. Appears to be the same as the one you have. Very classy tray and a great find - congratulation.