Not sure if it’s just a typo or another hamburger shop I haven’t run across before, but has anyone heard of this one?
The classified copy, from Dec. 20, 1941 reads as follows:
Young Man to work in hamburger shop. Apply Little Castle Shops, 750 Washington Blvd.
Legal Notice Nov 24, 1939
Co-partnership Notices
Notify the partnership heretofore existing between George W. Gash and J. Gilbeert Johnson a restaurant business at 750 Washington Boulevard, under the trade name Little Castle Shop and 2837 Greenmount ave under the trade name Little Inn has been discontinued, partitioned and liquidated by mutual consent. Effective Nov. 1 1939 George W. Gash, Gilbert Johnson
Edit 12/15/12: Another Little Castle Shop was located at 3707 Eastern Avenue Baltimore MD.
Diner Hunter 
Wow! 750 Washington Blvd. Unless I am mistaken, that is in the heart of Pigtown. I gotta go check out the location.
I looked it up on googlemaps, and it doesn’t look like there’s anything there any more. It’s a new one story brick building: Bon Secour- Washington Village.