COL Charles Beckwith aka; Chargin Charlie the US Army officer who started the elite SFOD-1 unit(Delta Force) hired a "fashion consultant" to explain to his operators how to conceal weapons & "fit in" with plain clothes details.
The novel; The Protector by David Merill(check spelling) went into detail about fabrics, holsters, concealment, etc. The main character was a ex-spec ops/Delta Force member who became a private security specialist/EP agent.
Clyde