Is 7 l8r than 9? (Is seven later than nine?)
Pyth - 11 bytes
Easy, uses ._ sign to get the sign and C to get char codes.
._-F_CMcz\-

Try it online here.
Test suite.
._               Sign of number
 -F              Fold subtraction (this finds difference of a tuple)
  _              Reverse list to get correct order of operands when subtracting
   CM            Map char, already treats strings as digits of base256 number
    c \-         Split by &quot;-&quot;
     z           Input