If f: R $\rightarrow$ R is signum function, then how is (−2f): R $\rightarrow$ R defined?

$(-2f)(x) = \left\{ \begin{array}{l l} -2, & \quad if \: x > 0 \\ 0, & \quad if \; x = 0 \\ 2, & \quad if\: x < 0 \end{array} \right.$