It seems to be the norm in American Kenpo systems. Almost every Kenpo school I have looked at has bars (either red or gold) for their black belts. Some systems like Nick Cerio Kenpo have stripes for brown belts.Americans like to boast and show off more than others it seems. I don't know when, where or by whom the blackbelt stripe thing got started. I think the only way to get a clue is to review numerous old photos from the 1940's and 50's of blackbelts from various styles or search thru old writings. That's probably too time consuming (unless one has a lot of free time and the interest to devote to it) so may remain one of karate's mysteries. I have the time but not the interest to research it.