It's usually reporting the disposition of the call they are assigned. 10-8R or Romeo/Robert means in service, report made, for example. Before 9/11, a lot of public safety traffic used all kinds of codes and not everyone's 10-codes were the same. They tried to get away from codes and use plain English so everyone was speaking the same language for the sake of interoperablility, but it's fallen away from that especially in law enforcement. As stated in a previous reply, they are department specific and probably not put out for public consumption like they used to in the old "Police Call" books.