I use the numbers but I think it stems from the days when kill didn't take
the names. It's easier for me to remember -1 and -9 than to remember what
the mnemonics are.
Same here - there first time I saw the mnemonics were in the built-in kill command in csh. Which was usefule for "kill -cont"
but to this day, since like Ron I grew on fifth/sixth/seventh edition which used numbers, the ones that I remember and care about are screwed into my fingers.
I never have an issue with -1 vs -9 with kill, but I do not have great story about how as a young engineer I wiped out the life's work of visiting professor because Tektronix had the 0 and 1 keys next to each other on one of the terminals they made. It was the console of our 11/60 and we had two RK05's and I fat fingured /dev/r...0 instead of 1. Bad stuff.