Yes, CACHETS is a Scrabble word!

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

Is it a valid word?

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

an indication of approved or superior status
a warrant formerly issued by a French king who could warrant imprisonment or death in a signed letter under his seal
a seal on a letter

Also: seal of approval, lettre de cachet.