And o7 as well :D (although o7 is IRC speak, not ham speak :P)

73?

It is a salutary morse code "prosign" on amateur radio

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/

It's proto-pager code: https://en.wikipedia.org/wiki/Wire_signal

https://www.pagercodes.com/common-pager-codes.html

'Best wishes' but in morse it takes less time to write 73!