Yes, FLASHER is a Scrabble word!

Letter values in Scrabble US: F 4, L 1, A 1, S 1, H 4, E 1, R 1.

Is it a valid word?

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

someone with a compulsive desire to expose the genitals
an electrical device that automatically turns a lamp on and off (as for an advertising display)
a light that flashes on and off; used as a signal or to send messages