Tesla has used space characters in internal emails to identify leaks
Ashlee Vance's biography of Musk (from a few years ago) had a fun similar story. Someone inside Tesla wrote a letter, I believe complaining about product defects, which was printed by a media outlet. Figuring that the leaker printed the letter at Tesla offices (i.e. likely didn't have a printer at home), Musk re-typed the letter in Word, found out exactly how many kilobytes a Word file with that exact text would be, then searched the printer logs for who printed a file with precisely that many KBs recently. Doing this, he found the leaker. (It's been a few years since I read the book so a couple of the details may be off, but that was the gist of the story)