Technically "right thumb, or left thumb if you have no right thumb, or another finger if you have no thumbs".
Which I remember only because I was surprised/amused to see this in the driver's handbook (the pamphlet they give you if you are applying for a license). That handbook contains a tiny slice of the vehicle code, presumably the most important subset, which is why this made me laugh.
I just looked at the current one online and it no longer includes this info.
Is this true for all drivers? When I moved to California and got my driver's license I don't remember having my thumb print taken. I've even considered it a badge of honor that I've never given my fingerprints to the man.
