Yours, Etc.: Origins and Uses of 8 Sign-Offs
"thief, burglar," especially "safecracker," 1903, underworld slang, of unknown origin, said to be from John Yegg, a Swedish tramp, or from German Jäger "huntsman."
A thief or burglar, esp an itinerant thief or safecracker
[1903+ Underworld; origin unknown; said to be fr the name of John Yegg, a Swedish tramp and safebreaker; perhaps fr German Jager, ''huntsman,'' applied to a safecracker's advance scouts, but originally yeggman]