On a recent trip to France and Spain I was approached twice by young girls asking if I spoke English. Once was in the Tuileries Garden in Paris and the second time was atop Montjuic in Barcelona just outside the museum. In Barcelona there were 4 young women who had a poorly mimeographed paper in English asking for help for deaf people. This is one time to be impolite and to immediately move on saying an emphatic "NO". I've heard from others that this is a ploy and people who stop are often robbed of valuables.
I have encountered young women asking me if I speak English outside of Notre Dame in Paris, on 2 different trips. I don't know what their scam is, but I just smile and shake my head no and keep walking.
I had the same thing happen in the Paris train station. A woman came up to my boyfriend asked if he spoke English and when he said yes took out a piece of paper asking for money for a sick family member. He told her if he gave her money he would have to give everyone else money too. She didn't understand what he said and left. Not 2 seconds later did another woman come up and ask if he spoke English. This time he said "no" and she left. It is obvious that someone wrote the note for these women.
Anyone who approached you who look like they are gypsies (the girls with long skirts) just walk by and tell them "no english" and they will leave you alone. They are gypsies and they are looking for money and usually surround you and will definitely try to pick your pocket or get their hands in your purse. Don't even give them the time of day. They will not follow you and they will move on to the next person. Also, if anyone comes up to you trying to give you a piece of gold that they say they found on the ground and they can't keep it for religious reasons just walk away. If you take it in your hand and then try to give it back, they can get quite nasty. If something doesn't feel right, it probably isn't. JUST WALK AWAY!!!!! Happy Travels!!
The only trouble I have ever had is with gypsies as Mark has said. In Italy I found them really persistent but a very strong NO while shaking your head plus walking away worked for me, and I was alone. On one other ocassion I just went into the nearest shop. In France I didn't find them as persistent and just said no and kept walking. Anything that seems like a scam probably is. I tend to trust my gut instinct.