The designations that you hear ALPHA, BRAVO, CHARLIE, DELTA, and ECHO, are known as part of the PMD coding system found here in Delaware and other places. There will often times be 2 numbers associated with the A, B, C, D, or E. Such as 29D4 which would be a MVC with rollover and a 31C1 Unconcious/Fainting. These are to help the responding units weather it be the ambulance, paramedics, or fire department understand with all the info the dispatcher has what is actually going on prior to their arrival.
I have decrypted some of their codes they use. Today listened and watched a DUI arrest on my street, from the traffic I have decided that the use the delaware code reference number to describe the crime. A 4177 stop refers to the section of delaware code related to the incident or in this case, DEL CODE § 4177 : Delaware Code - Section 4177: DRIVING A VEHICLE WHILE UNDER THE INFLUENCE OR WITH A PROHIBITED ALCOHOL OR DRUG CONTENT; EVIDENCE; ARRESTS; AND PENALTIES.