The Riemannian product \({\mathbb{M}}_1(c_1) \times {\mathbb{M}}_2(c_2)\), where \({\mathbb{M}}_i(c_i)\) denotes the 2-dimensional space form of constant sectional curvature \(c_i \in {\mathbb{R}}\), has two different \({\mathrm{Spin}^{\mathrm{c}}}\) structures carrying each a parallel spinor. The restriction of these two parallel spinor fields to a 3-dimensional hypersurface M characterizes the isometric immersion of M into \({\mathbb{M}}_1(c_1) \times {\mathbb{M}}_2(c_2)\). As an application, we prove that totally umbilical hypersurfaces of \({\mathbb{M}}_1(c_1) \times {\mathbb{M}}_1(c_1)\) and totally umbilical hypersurfaces of \({\mathbb{M}}_1(c_1) \times {\mathbb{M}}_2(c_2)\) (\(c_1 \ne c_2\)) having a local structure product are of constant mean curvature.