The important part of the signature consist of three fields
r - String: First 32 bytes of the signature
s - String: Next 32 bytes of the signature
v - String: Recovery value + 27
v was 1 byte, but since EIP 155 it can have an arbitrary number of bytes. For more uses only 1 bit should be enough.
A common approach is to split the signature in those three fields r and s as bytes32 and v as byte and pass them as parameter.
Another option is to pass all of the together as an array of 65 bytes.
There's a new experimental ABI encoder that allows tuples as parameters, you might want to pass around a tuple with those fields.