To do the sign for "idea" touch your
forehead with the tip of your pinkie ("I" handshape) then pull your hand out
and up into the air.
Memory aid: Think of a light bulb going on.
A variant of the "idea" sign is the sign for "IF / suppose."
This sign is good for introducing discussion topics.
Hold the right "I" hand an inch out from your right cheek. Touch the tip
of your pinkie to your right cheek, then bring the hand back out an inch and then
touch the cheek again.
Do NOT twist the hand.