In the latest issue of Guns and Weapons For Law Enforcement, Massad Ayoob, a tactics instructor & sworn LE officer, stated that LE officers should use neck chains or chest level badges. A large PD researched carry methods & found that badges on neck chains had the fewest "blue on blue" incidents in training.
I've used a badge-ID holder since 2002 or so. I purchased a black nylon badge holder from www.Galls.com
. I'm glad I used it. I also work armed with uniform shirts that say; SECURITY on the back. That way, LE or any first responders can clearly see who I am in a critical incident.
You may say; "hey, so what" but you don't know when some people see guns & wig out.