Those of us lucky (accursed?) enough to have a job in law enforcement talk in 10-codes on the radio. We don't talk in code when speaking face-to-face. The surest sign of a rookie is someone who speaks in 10-codes when not on the radio. I don't know the origin of the code system, and I know that it varies from state to state. What I might call a 10-33 (network is reserved for emergency traffic) here in Louisiana, someone else might call by a different code. The CB radio boys picked up the 10-codes during the Smokey and the Bandit phase of Americana, and the long-haul truckers used it over the roadways with some regional variations. 10-codes are a vital piece of the law enforcement culture.
One of the most used 10-codes is 10-8. When you go 10-8 you let your dispatcher know that you are "in service, available for call". Most codes have opposites. For example, the opposite of 10-8 might be 10-6. 10-6 means "Busy". As in "I am busy doing what you last sent me to do."
Dispatchers and supervisors respect those codes. The dispatchers have a sergeant there, usually an officer of great experience and knowledge. The sergeant knows that when you are - - working a wreck, for example, you might have eight or ten things going on at a single time. You have rubber-neck traffic to deal with, you have tow-trucks to deal with. Maybe an ambulance or two, and maybe a fire truck. You have relatives showing up, cluttering up your traffic, to pick up the walking wounded, or inquiring about the nearest hospital, or wondering where the tow-truck hauled the debris. Not to mention the paperwork. You are in fact, 10-6. Busy.
The dispatcher, on the other hand, has to clear her calls. She (all personal pronouns are generic) has a list of incoming calls that need attention and a list of units available to service those calls. It is her job to get units rolling to protect and serve the public, to assist the officers on a call by sending the assets the officer needs, and to keep the sergeant amused during a long shift. A sergeant and a dispatcher are partners, just like the two officers in the cruiser are partners.
But, the sergeant knows how busy a routine call can get, and when you are 10-6, he (again, all personal pronouns are generic) will prevent the dispatcher from giving the officer another call. Lets say, for the sake of this exercise, that I am in unit 920. The radio conversation might go like this:
Dispatch: "Dispatch, 920"
Dispatch: "Are you able to go 10-8?"
920: "negative. The ambulance just got here and I have a wrecker standing by. It'll be a few minutes. I'm still 10-6."
The sergeant might ask again in 10 minutes, but they won't give you another call until you are finished with the first one. We can only do one thing at a time, especially when that one thing actually has ten or fifteen things going on simultaneously. As soon as you go 10-8, you'll get the next call, and it will be a long night when calls start stacking on the dispatchers log.
All this to tell you about 10-codes, and to let you know that for the next several hours, I'll be 10-6 at the range.