Usually, you can find these guys near Eiffel Tower. They will ask you to sign a petition to help a charity of mute or deaf people. You will see some signatures of other foreigners to make it seem more legit. The thing is that that paper has some words in French and basically says that you donate some money to charity. So after you sign, they will try to force you to give them money. This is a big scam. The charity itself doesn't exist so they are just trying to make a quick buck. Once again just ignore these guys and keep walking.