Old German Item ? Found In US Lot

Found this in a lot of old US material and cannot find it listed in Scott.
Any clues as to what it is and any value. Thanks

It reads that it is 'to attach the frank by the sender.' So, it appears to be part of postal stationery, but not even a cut-square.

It is like the çut out top right corner of a postcard that says 'affix stamp here.' It appears it was used applying a meter mark instead of a postage stamp. The meter mark, likely, will have been larger and is missing the 'flag.'

Value, most likely, is zero, and that is rounding up.

It is the value portion of postal meter struck over the stamp-affixing box of a return envelope/card.
I agree with NSK, no value.

Add: Simlar in general format to this piece currently on ebay:

Thanks for the info.. Much appreciated