This is a definitly of a Czech origin, but I am not sure about it's usage.

I found the same example on one auction, and there it is described as a label.
"5h Franz Josef 1908 Prag Jubil. Ausstellung P Praha PPC (Jubilejni Vystava v Praze 1908) to Kladno.
Label Not Tied Narod Sobe 2."
