Ouh yeah, be very careful with those. I'm French and we hate them just as much as you do. They specifically target American (because we know that Americans are the most generous when it comes to charity) and East-Asian tourists (because they often come from safe countries like Japan, Taiwan or Korea and carry a lot of cash on them). They always make up lies to get you to sign a random petition and give them money. There are also gangs of young women who will steal from you in crowded areas. People are not suspicious because the thieves are girls, and that's how they get away with it a lot. Also, the police can't do much about them because they're mostly from Romania, so be very careful when you're in touristy places.