The National Gendarmerie or the National Police do not decide for road signs. The manager of the road concerned is in charge. If it is a communal road, it is the town council that has jurisdiction in the matter. In the other cases, it may also be the county council, the state or a private body. You should contact them (phone, mail or email) to explain your difficulties. Click on the following link to access the public services directory:
Public.