Most of them have a rubber cover that slips over the shaft. The guys at work call them "condoms". It doesn't slip all the way to the seal, so turning the PTO on won't really hurt anything. Some of the BX's have a plastic cover and with those you can't see the shaft without removing the cover. It just pops on/off. Years ago when we sold Deere, had a guy buy a 990. Soon as he gets home he's out playing on it and kept trying to turn the PTO on to make sure it worked. Well on a 990 you can't see the shaft from the seat so he made a seat switch bypass, turned the pto on, walks around the back of the tractor and said "hmm....wonder if if't making any power"....grabs the shaft, squeezes and broke several bones in his arm/wrist/hand.