POV motorcycle Question: Sgt Chopper pulls up on his new ride, you notice the license plate is turned sideways...legal or not?

That runs into improper display of a license plate. One of the AR 190s covers it (or used to). We would just give people a heads up. I never heard of an MP giving a ticket for it.

The only Texas law I could find with specific verbiage about plates is with regard to visability and the license plate light, where it states it must be clearly legible from 50 ft from the rear. (Transportation Code Sec. 547.322(f)(2): (1) illuminates the rear license plate; and
(2) makes the plate clearly legible at a distance of 50 ft. from the rear.)
The only other code I found was Transportation Code Sec. 502.409 and this basically refers to obstructing visability of the plates

CW3 Kevin Storm
Here in AZ they make no mention whatsoever of "vertical license plate placement" and in fact I see them all the time both on base at Davis Monthan AFB, out in town, and many of my CVMA brothers and sisters have their plate mounted like that.

For reference:
http://www.azleg.state.az.us/ars/28/02354.htm