  Let $S=(G, \sigma)$ be a signed graph where $G=(V, E)$ is a graph called the
underlying graph of $S$ and $\sigma:E(G) \rightarrow \{+,~-\}$. Let $f:V(G)
\rightarrow \{1,2,\dots,|V(G)|\}$ such that $\sigma(uv)=+$ if and only if
$f(u)$ and $f(v)$ are of same parity and $\sigma(uv)=-$ if and only if $f(u)$
and $f(v)$ are of opposite parity. Under $f$ we get a signed graph $G_f$
denoted as $S$, which is a parity signed graph. In this paper, we initiate the
study of parity labeling in signed graphs and we define and find `rna' number
denoted as $\sigma^-(S)$ for some classes of signed graphs. We also
characterize some signed graphs which are parity signed graphs. Some directions
for further research are also suggested.
