Thoughts on Wind Up Workin' In A Gas Station.

I found this on wiki jawaka and have a totally different view of these lines . . .

The thumb reference explains an obvious way to identify anyone who makes a living working on automobiles. Automechanics typically have black grease under the finger and thumb nails. In addtion, the thumb has a tendency to take some abuse in this occupation, and after a while will have a hammered on appearance. Sir Arthur Conan Doyle would be proud.
In addition, mechanics are seldom regarded as members of the intellectual elite, so the stigma of a black, scarred thumb could translate to "destined for a lifetime of failure and mediocrity". i.e. "Wind up working in a gas station"...

I don't think Frank is talking about a greasy thumb, I believe he is refering to the practice of giving a thumbs-up. Around this time this track was written, the teevee show Happy Days was big and The Fonz was known for throwing up his thumbs. It was/is a way of saying, "aw-right" or "cool." I believe what he is saying is, if you've been there, give me a thumbs-up.

Anyone else have any thoughts on this?