Len is a closet Morse Aficionado!

From http://www.ac6v.com/73.htm

ORIGIN OF HAM SPEAK - FACT, LEGENDS AND MYTHS??
Len Anderson retired (from regular hours) electronic engineer person Writes:
After 1844 (the year of the first commercial telegraph service in the USA,
Baltimore, MD to Washington, DC), the blazing speed of the early
electromechanical sounders made it necessary for commercial telegraphers to
to use abbreviations for standard phrases in telegrams. It gave telegraphers
a chance to send more telegrams during a workday, increase their profits,
etc., etc.

A whole bunch of different two-number sub-codes were invented and used. Few
survive to today since morse codes have survived only in amateur radio.

One of the enduring sub-codes is "73" meaning "Best regards." Hams use it on
voice, as well. It has become traditional jargon.

Morse code did NOT begin as the character = dot-dash group but was
originally ALL numbers! Morse got a financial and lab mentor in railroad
heir Alfred Vail who is reported to have suggested a change from the
all-number code to one where each letter, number, and common punctuation
mark has a unique dot-dash group. This latter improvement, along with a way
to increase the distance of a landline by using a "relay" of an
electromagnet whose magnetically-coupled switch substituted for a
telegrapher's key in an unmanned telegraph line relay station. Up to three
such "relays" could be used on a wired telegraph circuit. That may or may
not be the etymological origin of the word "relay" as the component we know
today.