According to Mary Perez, a reporter for the daily newspaper -- The Sun Herald -- here's the story behind the use of "Warren" on the Boomtown Casino's use of the name on the $5 chip.

Lifted from her article: Warren the bull is the good luck charm for players at Boomtown Casino.
Chris Foret, marketing manager, said regular players drop a quarter or a dollar into the bucket at the (life-size) bull’s feet for luck when they enter the casino. That money is donated to a charity every three months.