FWIW, returning from a patrol mission along the West German/Czechoslovakian border with the U.S. Army in the late 1980s, we took some time for the accompanying AH-1 to do a series of under-the-wires crossings. My impression was that it was box checking for a proficiency requirement. No lines visible in this picture, but it was during that activity, IIRC.
Bell AH-1F Cobra by
Mark Carlisle, on Flickr