[tmm]

Does anyone what the "international symbol dictionary" Susan Kare used was?

[robinhouston]

I don't know, and I'd love to.

If I had to guess, I'd guess Henry Dreyfuss's Symbol Sourcebook. It was published in 1972, and it seems plausibly the sort of book someone like Susan Kate might have had to hand in the early '80s. https://www.societyofsigns.com/projects/symbol-sourcebook

[wsh]

Symbol Sourcebook would’ve been my first guess, too, but I just glanced through my copy (7th printing, 1977) and didn’t see the ⌘ symbol. The closest thing in the Graphic Form Section is a symbol for “Atomic d orbital,” but it’s clearly not the same one that inspired Susan Kare.

[Vespasian]

Does anybody know of a modern day equivalent in the form of a searchable symbol database maybe even with a "freehand drawn" image search?

Unicode does not quite cover it because it lacks context and meaning of combined codepoints.