3 Kopecks

Russia's treasury issued these fractional notes in 1915 as a direct response to the near-total disappearance of copper and silver coinage from circulation — hoarding accelerated dramatically once war mobilization began and metal became strategically valuable. The solution was essentially a postage stamp printed on cardboard-weight paper, legal-tendered by decree. The reverse explicitly stated they circulated on par with silver coin of the same denomination.

At under 30mm in either dimension, these are among the smallest paper money ever issued by the Russian imperial government. Survivors in any condition above poor are genuinely uncommon — the notes were handled by everyone, worth almost nothing, and treated accordingly.