To sign subtract, hold up your non-dominant palm flat and horizontally (lying on its pinkie finger side) as it is facing you. Then take your dominant hand in the form of a claw, and touch its bent fingertips to the inside of your palm before shifting the claw into a fist as you pull your hand down away from the palm.
It is as if you are subtracting something from the page or paper you are holding up with your other hand.
Teach your toddler the subtract sign when you are teaching them basic Math at home.
This is a useful flash card taught best in conjunction with other counting or number-centered signs.