I don't think theses have appeared here on this thread yet.
They are
Philatelic Labels made available to collectors which if they were attached to letters and handed in at the Post Office counter or at special post boxes were supposed to be carefully hand cancelled with clear CDS.
Actually this label wasn't needed since most Austrian used stamps and covers have clear, sharp
CDS actually in many cases better than the example below.

I have 2 different examples, one light yellow & green and one
darker yellow & green.


I believe the German Post Office made similar ones also available to collectors.