"I am good"
* "I": Touch your chest with your dominant hand (the hand you write with).
* "Good": Make a "G" handshape (thumb and pinky extended, other fingers closed) and move it forward and slightly upward in front of your chest.
Or
"I am well"
* "I": Touch your chest with your dominant hand.
* "Well": Make a "W" handshape (all fingers extended and spread) and move it from your chest out in a circular motion.
Or
"I am okay"
* "I": Touch your chest with your dominant hand.
* "Okay": Make a "O" handshape (thumb and forefinger touching, other fingers closed) and move it in a circular motion in front of your chest.
Remember that the most appropriate sign will depend on the context of the conversation and the level of formality.