At the request of Juan Carlos, LU9DO, AMSAT-LU wanted a series of APRS designators for uniquely identifying AMSAT APRS applications. He suggested those beginning with the letter O for OSCARS.
ALL APRS applications include this identifier in their packets so that the source of APRS data can be known. See the list at
APRS UK Yahoo Group http://groups.yahoo.com/group/APRSUK