Mag switches are up for 'live'. In this position, the swith is 'off', or 'open circuit. When they are down, the switch is 'on' completeing the circuit to ground the magneto and thus disable it.
This is a failsafe system in that if the switch fails, or the wiring to the switch, it goes 'open circuit' and the mag is 'live'. If it worked the other way around, any fault in the switch or wiring would result in an engine failure!
But it does mean you should always treat a prop as 'live' if you are turning it by hand. If there is a fault in the switch or wiring, the plugs will spark and the engine could start.