Really? Weird. I swear that's the way I always see it abbreviated, though I think most recipe sites that I use just spell the whole thing out- so maybe I just don't see the abbreviation that often.
For what it’s worth, what I see in recipes is usually T for tablespoons and t for teaspoons. (But the cool kids are switching to g and mL, especially for baking.)
Very fun! I don't think this will stop anyone from solving the puzzle, but the title character of 4-A is actually a criminal mastermind - they're the character who the globetrotting mystery solvers in the story are constantly thwarting.