Violette / Marcel Violette
Thanks to Joe L for sending these pictures.
The letters "JJ" are stamped on the underside of the long E key (left pinkie key). It was sold to me by my teacher (in the 1950s) who was 1st clarinet with the Philadelphia orchestra and a gentleman of the highest caliber.
From the appearance of the keys, I am guessing that this is a Thibouville product.