[Canada Kev]

So I did some research. Regardless of the lens colour, in the US, lenses are supposed to be stamped DOT to indicate they comply with the Department of Transportation standards. So if you had turn signal lenses that are yellow and have the DOT mark permanently embedded into the lens, they would be legal. But you probably won't find any because 911s were never available new with those tail light lenses in the US market and an aftermarket company likely won't have the resources to certify new lenses in yellow to be tested and certified to comply with those standards. Plus, I believe DOT standards requires them show some portion or red light and reflector at the rear of the vehicle to be visible from the side.

Perhaps someone that has URO or another aftermarket lens that is all red can check to see if they are stamped with the DOT mark. Because to be officially, completely legal in the US, they should have it. I suspect that they will as URO (and others) probably just took an impression of existing lenses to create their casting molds.

As a side note, my URO replacement front signal lenses do have the DOT mark, so that lends some support to this supposition. The yellow signal URO replacement tail lenses I have, as well as my factory original Bosch Euro units (RoW car), do not show the DOT mark, but they have the E1 stamp.

In Canada, the DOT mark is accepted as proof they comply here, as are lenses with the E stamp indicating they comply with ECE standards. I also believe that lenses meeting DOT standards are, interestingly, also legal in European countries.