little yellow bird with tag

Hello,

This little bird has been hanging out in my back yard for the past two days. I suspect its a female yellow finch but I'm not sure. She comes towards me when I come out and doesn't seem afraid of people. She also has a tag on her leg. The cat that lives in my house seems really interested so I'm worried about the bird being here. 

I'm wondering what the tag might be about and whether it is actually a yellow finch.

Thank you very much,

Itir