You've probably seen or read about the creative beggars who push a petition in your face, asking for your signature and a donation. This morning my wife grabbed one of the forms they want you to sign as the perp fled the Place de l'Hotel de Ville this morning:
Of course it's a scam to get you to give them money or sometimes a cover/distraction to keep you busy while their colleague picks your pocket. Either way, there is no reason to sign ANYTHING in France if you aren't a registered voter and/or citizen of the country. Walk on by and don't even acknowledge their existence. They are invisible to you.