  For a spanning tree T of a connected graph G and for a labelling \phi: E(T)
\rightarrow {+, -}, \phi is called an alternating sign on a spanning tree T of
a graph G if for any cotree edge e \in E(G)-E(T), the unique path in T joining
both end vertices of e has alternating signs. In the present note, we prove
that any graph has a spanning tree T and an alternating sign on T.
