Being painted red, I'd first suspect that it was for the heating system, or perhaps an electric water heater. It may be no longer in the circuit.
Have you tested the connections to see if there is any voltage there?

I would also vote for the remote cutoff on an oil burner or other heating. There is/was apparently a requirement to have a remote power cutoff if you have an oil burner, since these switches have been installed in two of my houses in Northern VA (one built in '78 and one built in '40). They are red and usually at the top of the basement stairs or the rear entry, but I guess they could have put one in the living area.

Bruce