The call signs "7-Mary-3 and 7-Mary-4, responding" meant that cops from which US TV series were on their way?

The American television drama series "CHiPs" that originally aired on NBC from September 1977, to May 1983 followed the lives of two motorcycle police officers of the California Highway Patrol (CHP). In 139 episodes spread over a total of six seasons, the urban police experiences of officers Francis (Frank) Llewelyn 'Ponch' Poncherello (Erik Estrada) and Jonathan "Jon" Andrew Baker (Larry Wilcox) were seen by a very receptive and large public audience. The code names for these officers were 7-Mary-3 for Jon and 7-Mary-4 for 'Ponch'.

As media critics noted, what was truly enlightening and present in almost every episode was the way that key characters showed some of the personal and professional efforts needed to put typical lawbreakers and hardened criminals behind bars. Rewards for the actions taken by the officers were also properly noted.