Representation of ZERO (in 8 bit) :
In signed magnitude : 10000000 and 0000000 which are -0 and +0 respectively.
1's complement : 11111111 and 00000000 which are -0 and +0 respectively.
2's complement : 00000000
Note : Representation of ZERO is the reason why range of 2's complement is one more than range signed and 1's complement.