Yes, even when you know you are 100% wrong, NEVER sign anything. Even if they insist, no one can force you to sign. I am not only talking about the wearing of the mask or the lockdown but also about speeding or any other offense. Also make sure to request, in cases of speeding, the serial number of the radar and its date of calibration (radars must be calibrated once a year).
You fill in a statement giving any reason and if they refuse it, you dispute it by not signing (signing is accepting)! Note that as long as you dispute, they cannot apply a second fine!
SI NOUS CONTESTONS TOUTES NOS AMENDES POUR DEPLACEMENT, LE SYSTÈME VA VITE ÊTRE SATURÉ. RESISTANCE !