Use your forefinger to trace ordinary block capital letters boldly on the palm of the deafblind person's hand, each letter directly on top of the last. The Block Alphabet is a tactile method of communication which is used to communicate with people who have little or no residual sight and hearing.
For yes, two taps on the palm of the hand.
For no, or for erasing an error, a rubbing out movement across the palm. Letters should generally be drawn from left to right and from top to bottom.