Your stamp is perf 11, thus in can only be Scott 514, which is unwatermarked, although an unusual shade.
Your stamp is printed by the flat plate method. The ink on the back is "set off" from stacking damp sheets and the slightly wet ink from one sheet imprinting on the back of the next sheet. Quite normal.
The front of the stamp is canceled with a double oval cancel typically used on parcel post and registered mail. It contains the name of the city, perhaps MEMPHIS / TENN, or similar, of the style here: