This is the sought after stamped Mutterkreuz / Motherscross stamp, of course on the original 2. Kriegs-Muttertag Iglau postcard.
The reason for this card (and desirable stamp!) being so rare, is that it was only in use for one day -> Mothersday 1941 in the Protectorate of Bohemia and Moravia (current day Czechia).
In good condition and very very hard to find!
This is a must-have card for any Motherscrosscollector!!!