I've seen the word Hashem hyphenated ("Hash-m"). Is there any valid reason for this practice?
The names of Hashem which may not be erased are listed in Shulchan Oruch Yoreh Daioh 276 (9).
Hashem is not one of them and so the hyphenated ("Hash-m") seems unnecessary.
Hashem is what we use in place of one of the Aibishter's holy names. It simply means The Name. Perhaps people generalize from the examples of G-d and L-rd, and replace the e with a hyphen.