This is something you don't see very often (at least I don't).
An impression of a design offset onto the gum of a pair of second issue revenue stamps.
My best guess is that the gum on the stamps was only partially moistened before it was applied to a document of some kind. Somehow, a considerable amount of ink from that document was transferred to the gum of the stamps, and then the stamps must have fallen off of the document. Clearly, the stamps were never soaked off, as the design would have then disappeared.
Kind of a weird thing to see.
Jim

