German 12 Pf Day Stamp, 1945

All I know about this stamp is;

1. 12 Pfenning Denomination,
2. It has Original Gum but Hinge remnant,
3. Believe it was issued in the Russian Zone, OPD Schwerin,
4. Believe I read that it is called a Day Stamp.
5. Crude measurement is 19 x 22.5mm

I got it in an auction box I won the bid on in a little store called Charleston Stamps, here in Las Vegas, Nevada, USA