16 Year Old Girl, Birthday Present?? Anyone Know Anything About Signet Rings, Maybe?

I’ll be 16 in under a month and my parents are already asking me what I want. I bought a laptop just before Christmas, I got a phone last birthday, and my iPod is still in decent condition. Mum said that for my older sister’s 16th she was given a ring, but I don’t know anything about jewellery so I’m not sure if I’d be able to appreciate it as much given my lack of knowledge. If I had to go jewellery, I was thinking maybe a simple signet ring with amythest or something, as that’s the only type of jewellery I could constantly wear. But I still know nothing about that, and I can’t find any decent sites.
I don’t really need makeup, and Mum always complains that she doesn’t know what sort of clothing to get me. We’re also going to Europe in June, so I’ll probably look for clothes and stuff there. There aren’t really any DVD box sets that I want, and I’ve got no idea. My favourite bands have all been broken up for at least 5 years and I have no idea! I don’t play any instruments, though I’d love to play guitar, but I’m not sure if I’d have the time to learn it because of Grade 11 exams, holidays and part-time work. Please help!