The signum function is the D4948: Integer function $$\begin{equation} \mathbb{R} \to \{ -1, 0, 1 \}, \quad I_{(0, \infty)} (x) - I_{(-\infty, 0)} (x) \end{equation}$$

The signum function is the D4948: Integer function $$\begin{equation} \mathbb{R} \to \{ -1, 0, 1 \}, \quad I_{x \in (0, \infty)} - I_{x \in (-\infty, 0)} \end{equation}$$

The signum function is the D4948: Integer function $$\begin{equation} \mathbb{R} \to \{ -1, 0, 1 \}, \quad x \mapsto \begin{cases} 1, \quad & x \in (0, \infty) \\ -1, \quad & x \in (-\infty, 0) \\ 0, \quad & x = 0 \end{cases} \end{equation}$$