Money order cutter
Post Office Department money order forms in the 1920s and 1930s had values printed along an edge. This tool was laid over the form and higher value amounts were torn away along the edge leaving the value for which the money order was to be issued. This was an effective anti-tampering approach since the form could not be forged to create a higher value than the amount still showing. Applying a post office validation imprint that included the post office name, state, and "MOB" for "Money Order Business" activated the money order.