#char is a ZZT-OOP command for changing an object's display character. It takes a single parameter, a decimal number from 1 to 255, representing the desired extended ASCII character.
Note that #char does not allow character 0 as a parameter, even though it is a valid extended ASCII character. Running
#char 0 will silently fail without changing the object's character. This restriction does not typically matter in practice because characters 32 and 255 are usually visually identical to character 0.