can we know the sign of a ciphertext (homomorphic) Is it possible to know the sign (positive or negative) of an homomorphic ciphertext particularly under paillier scheme ?
Pallier encryption works over the finite ring modulo $n^2$.  The distinction between positive and negative numbers don't exist there (or in any finite ring or field), so there isn't really a sign that works like the sign of integers.
Of course you can use signs in the notation, e.g. $-1$. But that is just the same element as $n^2-1$. Both represent the same residue class modulo $n^2$.