The only two I know are: Code-R, which is usually used in conjunction with dispatching move-ups and instructing them to use lights and sirens due to a large incident; and Code-I, which I haven't heard in a while, but it means a request to dispatch a PIO, Public Information Office, to a large or significant incident. Interestingly, I happened to be watching an old episode of Emergency yesterday where Gage and DeSoto were being shot at during a rescue. Captain Stanley advised "L.A" of the situation and requested a "Code-L", which meant he needed law enforcement at scene. I have to say, I've never heard that one. The on-scene captain usually just "Requests Sheriff".