Suppose I am out in the wilderness and an emergency arises. I have an accurate fix on my location (from GPS, map and compass, astronomical observation, etc...). I manage to get in touch with emergency services and need to tell them where I am.
But there are many different formats I could use to report my position.
Latitude and longitude in degrees / minutes / seconds
Latitude and longitude in decimal degrees
Latitude and longitude in degrees and decimal minutes
(And with any of these systems there is the finer question of which Earth ellipsoid or datum my map or GPS is based on, which could make a difference of a few tens or hundreds of meters in the position; in dense forest this could make it considerably harder for rescuers to find me.)
Obviously I want to avoid any confusion; if I give my position in (say) degrees / minutes / seconds, and a helicopter pilot blindly types it in their GPS which is set to decimal degrees, they'll go to the wrong place (perhaps many kilometers away). UTM is less ambiguous, but will they even know what that is? I may be speaking to a dispatcher in an urban office, perhaps over a noisy and unreliable phone or radio connection, and that's hardly the time for a technical discussion of the fine points of geodesy.
So in short:
Is there a particular position format that's preferred by emergency responders?
Are dispatchers and responders sufficiently trained to understand the difference between these positions, so that I can use any format if I tell them which one it is?
Are there other general "best practices" for this situation?
I suppose the answers may differ between different countries or regions (I'm in the US) or between land and sea emergencies (I'm usually on land).