I've always thought the non-U.S. bikes had a cleaner look to 'em, but had always head that there was a Federal reg against that.
In a spat of curiousity I poked around & finally found it.
In case you've ever wondered you can find it here
https://www.gpo.gov/fdsys/pkg/CFR-2004-title49-vol5/xml/CFR-2004-title49-vol5-sec571-108.xmlThe verbiage is pretty specific:
Horizontally, turn signals must be:
At or near the front—1 amber on each side of the vertical centerline at the same height, and having a minimum horizontal separation distance (centerline of lamps) of 16 inches. Minimum edge to edge separation distance between lamp and headlamp is 4 inchesAt or near the rear—1 red or amber on each side of the vertical centerline, at the same height and having a minimum horizontal separation distance (centerline to centerline of lamps) of 9 inches. Minimum edge to edge separation distance between lamp and tail or stop lamp is 4-inches, when a single stop and taillamp is installed on the vertical centerline and the turn signal lamps are red.
Vertically:
Not less than 15 inches, nor more than 83 inches.
Since the rest of the world gets by without it I think it's a bit silly, but as the French cest...la vie.