This page is designed to calculate the correct PI code value for your station's callsign.
The R(B)DS standard assigns specific Program Identification (PI) codes to each U.S. station, mapping them from the call letters. The point is to ensure two stations with the same service area don't end up with the same code. Otherwise, it is theoretically possible some radios might regard these stations as interchangeable, and automatically tune between them when one's signal fades.
My ulterior motive: I'm a TV engineer -- but also a long-distance reception enthusiast ("DXer"). The RDS PI code is invaluable for this pursuit. It is transmitted more often than any other piece of information in the RDS datastream - and far more often than your stations legal ID, or even any identifying promos/liners/etc... By transmitting the correct PI code, your station can be identified even if it's received via a 1-second reflection off a meteor trail.