droits réservés (maybe not a valid publisher; the term "droits réservés" means "rights reserved")

Not a label but a term use when the publisher is not known.
"In the field of publication, droits réservés (or DR) is a notice affixed in place of the credit of the author of an orphan work, that is to say a work of which it is impossible or difficult to identify the author. If the author is subsequently identified, the publisher can then compensate him and restore authorship of the work to him."
https://fr.wikipedia.org/wiki/Droits_r%C3%A9serv%C3%A9s