Used to determine if numbers shall be converted to signed or unsigned strings by the word N>S.

TRUE UNSIGNED !
-1 N>S TYPE CR

(displays 65535)

FALSE UNSIGNED !
-1 N>S TYPE CR

(displays -1)

When executed, returns the address of the UNSIGNED variable so that it can be accessed as a variable with ! and @.

Internally, words such as . U. .R and U.R manipulate the UNSIGNED variable in order to force N>S (number to string) to convert the numeric value in the appropriate signed or unsigned format.