Just trying to help out those who have not heard of these scams.. they are not new, and they are fairly common.
In both cases your ability to IGNORE strangers .. WALK on,, and NOT respond at all will keep you safe.. but most of us are used to answering people when spoken to.. or trying to help people. In Paris, just don't.
The ring scam is simple. You are walking along and someone ( can be man or woman ) will stop in front of you with a ring in their hand.. they will proclaim they just found it.. they may ask if it is yours( especially stupid when you consider they are in front of you .. so how would your ring get lost in front of you ..lol). They will then offer you the ring.. they will make up some tale that they cannot keep the ring.. its against their religion or some such thing.. and while you are now holding the FAKE gold ring they will then ask you for some money.. after all,, you have the "gold" ring.. isn't it worth it to give them 10 or 20 euros.. its obviously worth so much more.
ITs not , its polished brass. DO NOT STOP to chat in first place,, but if foolish enough to do so.. at least DO NOT allow them to hand you the ring or touch it.
The petition girls.. and they usually are youngish females.. will often be outside some touristy site.. asking people to sign a petition that has some vague cause like "to help deaf people" or " to keep children off drugs" etc.. They may start with a simple "do you speak english?" . WALK ON .. do not stop for them. .first off.. once you sign this phoney petition they will demand some money..making you think you HAVE to donate.. and secondly.. as they are now standing close to you.. there may be a few of them, one will try and pick pocket you while others distract you.
These scams are easy to avoid if you can simply learn to walk on,, don't slow down, do not respond to their "do you speak english"( think about it,, in your country do your petition gatherers walk up to tourists and say "speak Japanese" or "speak German" and try and get the tourists to sign petitions.. no of course not for goodness sake,,only citizens signatures are good on petitions anyways.. not tourists...