In our theoretical investigation for small Ag-Au alloy clusters, we found that pronounced polarization of their electrostatic charge occurs with some generic regularities. We propose a set of "rules" for the charge distribution, which may be extended to larger Ag-Au alloy clusters or even bulk solids: (1) atoms in lower-coordinated sites tend to be charged more negatively or less positively; (2) the charge of Au is affected by nearest neighbor atoms only, contrary to the case of Ag. The origins of these phenomenological rules may include site-dependent electronic polarization and the difference in s/p hybridization between Ag and Au.