It is a salutary morse code "prosign" on amateur radio https://en.wikipedia.org/wiki/Prosigns_for_Morse_code https://en.wikipedia.org/wiki/Prosigns_for_Morse_c

It is a salutary morse code "prosign" on amateur radio https://en.wikipedia.org/wiki/Prosigns_for_Morse_code https://en.wikipedia.org/wiki/Prosigns_for_Morse_code edit: I may be overstating that the token is precisely a prosign. But if so it will be one of the closely related early electrical communication codes. https://hamradioprep.com/what-does-73-mean/ https://hamradioprep.com/what-does-73-mean/