Still, :S
Do you mean make them display on the board, or how to change?
To change, go to 'My Controls', then on the left hand side, in the 3rd light grey box down should be 'Edit Signature'
To view, do the same, except don't click Edit Signature, in the 4th box down is 'board settings' click that, then in the 2n'd central box down, there are a list of boxes... Enable the option to view member's sigs there.