You seem to have asked this question via multiple channels, and I’ll answer it via one of the others (I’ve not included a link because it’s not public). Feel free to post a summary of the result here once we’re done.
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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"
typeApplSignature is the creator type code (OSType, aka 'four-char-code') from classic Mac OS days. Modern macOS has some legacy support for it (see CFBundleSignature), but your client apps really ought to be using bundle ID (typeApplicationBundleID) or other modern identifier by now.