botberg: Bas
You do have an emergency switch, the power switch. If you cut the power during any operation of the "X,Y,Z steppers, all instructions to the switcher stop. It may cause a clog in your extruder, and would have to be cleared, but that would be a small price to pay, rather than possibly damage a motor. The ramps board has a small pushbutton switch on the board ,right side looking in, that will recycle the firm ware. I presume that there are pin outs on the board that would allow one to add a remote push button if throwing the power switch makes one cringe. That pushbutton is duplicated in the firmware on the LCD as "reset", but when the machine is acting up it is almost impossible to dial in "reset", so I just cut the power and it doesn't seem to cause problems. You can test this out by setting the LCD to Rehome after moving the steppers by hand to the far position and cut the switch in mid homing.