“…Closely related to the present paper are the work of Zaslavsky [12,13] and our recent paper [6]. Zaslavsky introduced some basic concepts of signed graphs such as circuit, bond, orientation, switching, incidence matrix, Laplacian, etc., and obtained an analog of the MatrixTree formula for graphs for unbalanced signed graphs; see [12]. Based on the work of Zaslavsky, the authors introduced coupling, characteristic vectors, circuit lattice, bond lattice, etc., and obtained the relations between them; see [6].…”