Let D be a finite digraph with the vertex set V(D) and arc set A(D). A two-valued function $f:V(D){ ightarrow}{-1,;1}$ defined on the vertices of a digraph D is called a signed 2-independence function if $f(N^-[v]){leq}1$ for every $v$ in D. The weight of a signed 2-independence function is $f(V(D))=sumlimits_{v{in}V(D)};f(v)$. The maximum weight of a signed 2-independence function of D is the signed 2-independence number ${alpha}_s{^2}(D)$ of D. Recently, Volkmann [3] began to investigate this parameter in digraphs and presented some upper bounds on ${alpha}_{s}^{2}(D)$ for general digraph D. In this paper, we improve upper bounds on ${alpha}_s{^2}(D)$ given by Volkmann [3].