"One-adam-twelve, one-adam-twelve, we have a 211 in progress at Dodger Stadium..."
Adam-12 was a police series on NBC from September 1968 to May 1975. The half hour show featured officers Pete Malloy and Jim Reed in a typical day as they patrolled the streets of LA. Adam-12 was one of the first cop shows to cover some of the more realistic problems law enforcement had to deal with, such as racial tensions, child molestation and anti-police attitudes of younger people. The television viewer spent the show as an observer in the squad car.
Officer Pete Malloy, played by Martin Milner, was the older more experienced cop while officer Jim Reed, played by Kent McCord, was the younger cop with the latest up to date training. They worked out of Rampart Station on the show. Rampart was also the name of the hospital on the TV series Emergency!. Adam-12 & Emergency! were both created by Jack Webb of Dragnet fame. Both shows crossed paths when Reed and Malloy would meet for a common matter at Rampart Hospital where they would compare notes with the paramedics of Emergency!.
"Adam-12" was the radio ID that the officers used when they were being dispatched by headquarters. The "one" at the beginning of the call was the division they were assigned to. "Adam" is the LAPD designation for a two officer unit and 12 was the area of the city they were working in. They were seen all over the city though, from downtown LA down into the valley.
Sources:
"Adam-12" (http://us.imbd.com)
Adam-12 (http://www.tvtome.com)