A lot of morse encryptions were devised by the old telegraph operators to encrypt common phrases. 53 = All my love. 54 = Merry Chistmas, etc.
These would be comon telegraph messages phrases. It resulted in shorter traffic packets.
The CB radio craze took on a lot of these numbers like 73s, etc.
I just find it funny that old 1800's telegraph operator's encryptions like L8R, 2DAY and 2MRW are used by youngsters who think that they're clever, modern and hip!!