"C-code" is actually SECODE, a brand name device for Sequential Coding & Decoding. It starts as a continuous tone interrupted by breaks in the tone of a particular duration. This was usually done with the old basic line interrupt used by the same mechanical rotary pulse dialer old telephones used. By counting the interruptions, you can tell by ear what number sequence someone is dialing.
The frequency used by NC law enforcement agencies was definitely 155.190 mHz, was a base-to-base only freq (no mobiles licensed in NC), and the audio tone frequency was 2205 Hz, if I remember correctly. The UHF and VHF Med channels originally had this device in hospitals (especially 155.340) and ambulances so they didn't have to monitor open channels and the units didn't have to have a particular PL frequency. When the correct sequence was decoded by a particular unit, it either disabled the receive PL at the radio being sought or simply turned on a speaker. Us old radio heads knew the number sequences for most of the surrounding SECODE users, so when we heard the dialing going on, we immediately knew who was being called.
Needless to say, this old technology is no longer in use, was displaced by the computer networks and now the internet and other comms, and the frequency is no longer a statewide requisite for law enforcement agencies. In fact, there are now some individual counties and municipalities in NC licensed for this freq as primary and tac freqs. Not likely you'll hear any department(s) using it as it was once used. The 154.875 freq is mostly a western NC thing and is more recent than the 155.190 thing of the 50s thru 70s. The western counties on VHF (the huge majority) and most of the ones on UHF make quite a bit of use of this freq, while there are a few individual departmants "down east" that use 154.875 as a primary frequency.