Yes, WATCHERS is a Scrabble word!

Letter values in Scrabble US: W 4, A 1, T 1, C 3, H 4, E 1, R 1, S 1.

Is it a valid word?

WATCHERS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a close observer; someone who looks at something (such as an exhibition of some kind)
a guard who keeps watch
a person who keeps a devotional vigil by a sick bed or by a dead body

Also: security guard.