What is this remarkable piece on the background?

Designed and engraved in 1935 by Achille Ouvré, this stamp is the third and final issue in the series, following the 1935 blue and the 1936 red.
This fiscal vignette was used to certify payment of the radio license fee and was to be affixed to the back of the radio set, canceled by the post office at the location where the wireless receiver was kept.
Already rare on cover or used, it is extremely rare in full sheet form.