What prosign is sent to indicate the end of a formal message when using CW?

In Morse code, prosigns are unique procedural signals formed by running two letters together into a single continuous character. They are essential for managing the flow and structure of a conversation. The prosign 'AR' is universally used to indicate the end of a formal radiogram message. When sending casual traffic, 'AR' can also be used to signify the end of a transmission before turning it over to the other station. It simply means 'I am done with this specific message.' It is easy to confuse 'AR' with other common prosigns. 'SK' is used at the very end of an entire contact (signing off), 'BK' is used for a quick break or rapid turnaround, and 'KN' is an invitation for only a specifically addressed station to respond.