It *looks* like the power shutoff switch, but I doubt it unless your batteries are in the back.
I don't think the 12V tank heaters were an option in 2010.
It *could* be a 110V water heater switch (if you have the 2 way water heater.)
Lots of guesses. Does it switch 110V or 12V wire? Can you see what the wires go to, or at least the direction they head in? Any clues in the power distribution center from the fuse/breaker labels? What happens when you toggle it? Can you ask the previous owners?
Doug and Karen
2014 Escape 19'
2005 Toyota Tundra V8 Access Cab