$$ \widehat{\text {Skew}}_{i, t}=\frac{3 \cdot\left[\hat{\mu}_{i, t}-\operatorname{median}\left(r_{i, d, t}\right)\right]}{\hat{\sigma}_{i, t}} $$
is called Low Moment Skewness by Baltas and Salinas (2019) who don't give a citation for this alternative measure of skewness. What is its source, or where else is it used?
Others call it the Pearson 2 skewness coefficent.