  Recently Naserasr, Sopena, and Zaslavsky [R. Naserasr, \'E. Sopena, T.
Zaslavsky,Homomorphisms of signed graphs: An update, arXiv: 1909.05982v1
[math.CO] 12 Sep 2019.] published a report on closed walks in signed graphs.
They gave a characterization of the sets of closed walks in a graph $G$ which
corespond to the set of negative walks in some signed graph on $G$. In this
note we show that their characterization is not valid and give a new
characterization.
