As far as I'm aware neither the French ULM registration details nor the call signs are in the public domain - which I've always found odd as the CDN, CDNR, CNRA, historique and planeur registration details can be accessed on the DGAC website.
Displaying the call sign on ULMs seems to be becoming increasingly more common nowadays.
What I do find odd is that ULMs display their registration letters and numbers on the underside of the wing but not on the fuselage - contrary to the practice for all other French civil registered aircraft. Is there a reason for this and, if so, does anyone know what it is?