Signed

When using the signed hexadecimal number system in programming (such as 68000 assembly), the values $80 to $FF are interpreted as -$80 to -$01 respectively. This is because there is no way to literally prefix a number with the minus symbol "-". Instead, the highest bit in a byte is used to represent negativity.

Conversely, the unsigned number system has no negatives. So $81 is read simply as $81.