What is SIGN() ?

Answer:

SIGN() is used to determine whether the specified is positive, negative or zero. In case of positive, negative and zero it returns +1,-1 and 0 consecutively.

print sign(0) -- prints 0

print sign(10) -- prints 1

print sign(-10) -- prints -1

Sometimes before using SIGN(), you need to confirm you are passing numeric value as argument.
You can do this using, ISNUMERIC()