First off, I don't think this is a particular popular mod (only seen one other bike on youtube do it) as it requires you to drill a couple wire exit holes into your subframe and have a seat (custom or Thruxton) that exposes the ends of the subframe.
But, if you're like me and constantly looking for ways to bob and slenderize your bike, I think this makes for nicely hidden, but functioning indicators in the rear. I used the same 3/4" LED clusters for front indicators, making a bracket that neatly tucks them in right underneath my smaller bottom mount headlight. Got the inspiration to do this from a Chop Cult Metal Shop article. All pretty simple to do. Video link below.