(1)

\begin{align*} \sgn\left(x\right)H_{0}\left(x\right) & =\begin{cases} 0 & x\leq0\\ 1 & 0<x \end{cases}\\ & =H_{0}\left(x\right) \end{align*}

(2)

\begin{align*} \sgn\left(x\right)H_{a}\left(x\right) & =\sgn\left(x\right)\left(H_{0}\left(x\right)+a\delta_{0,x}\right)\\ & =H_{0}\left(x\right)+a\sgn\left(x\right)\delta_{0,x}\\ & =H_{0}\left(x\right) \end{align*}

(3)

\[ \pm H\left(\pm1\right)=H\left(\pm1\right) \]

(4)

\begin{align*} \mp H\left(\pm1\right) & =-\left(\pm H\left(\pm1\right)\right)\\ & =-H\left(\pm1\right) \end{align*}