Looks like the Apple Lisa had this symbol on its standard keyboard (sans the word option), meaning it's been in use since at least the early 80's. I would wage

Looks like the Apple Lisa had this symbol on its standard keyboard (sans the word option), meaning it's been in use since at least the early 80's. I would wager that this was the first use of the symbol to denote this purpose. Interestingly enough, the symbol hasn't been widely explicitly mentioned in menus in Apple's OS until relatively recently (OS X). Option was always that special easter egg of a key that half of Mac users still never used or realized existed.