You will not find anything in the FMS or placards simply because there is no certification requirement to do so.
As a Guide
General the UK NATO would be referred to as a NATO connector. Airframes that were or have been used by Military or aerial work tend to have the NATO connector fitted for obvious reasons. Eg the Hughes 500 or BO105 was originally designed for Military use. These of course are US manufactured but deployed world wide.
The US NATO as referred to is generally used in US manufacture helicopters airframes originally intended for civilian use eg R22.
Sometimes you may also find that the US NATO’s may have been replaced with a standard NATO socket where it’s been adapted for Police Role work eg MD902.
You can tell by just looking at the face of the socket but unfortunately that comes with experience. Also, you should feel a positive click as you fit the plug into the socket. NATO into a U174 (US NATO) will just not feel right. With practice and experience you will learn to identify this within seconds.
Helmets would normally be ordered with a standard NATO because professional working aircraft with crew requiring helmets eg Pipe Line, Police Military etc would normally have NATO sockets fitted. These guys would normally only be flying one airframe type so no problem.
If you fly numerous types then you MUST carry adapters in your flight bag to avoid any embarrassment.
Adapters are available at the DC website if you have difficulty in finding one locally.