To elaborate on what I suspect this poster is conveying, keys in hand means the fob(s) of the keys in the palm of the hand and the hand made into a fist with each key on the ring poking out from between each pair of fingers.
Self-defense sites typically pan this approach, but if I were left with no other option, I might give it a whirl. For example:
http://novaselfdefense.com/blog/can-my-keys-be-a-weapon