I imagine that if a mechanic does something nice for you he's just doing a good job. It's a good indication he likes you, but nothing more. Some guys like to be respectful and considerate of women (as strange and "sexist" as that sounds today.) If he is particularly chatty, or compliments you, stands close, eye contact, etc. he might be interested. He might be interested and do absolutely nothing, but that doesn't help, obviously.

Some working guys take off their ring to avoid injury, or smashing up the ring.

If you brought him cookies he would love you forever. Cookies=Love. All the guys in the shop would love that. I promise you it would make their day.

I'm pretty much a total failure in this area, as I'm shy and not so comfortable approaching women. However, I believe that Copper Star is right. I constantly hear women talking about "creeps" and "jerks". Now there may in fact be a lot of creeps and jerks, but when you hear it so often it has an effect.