Yes, PIN is a Scrabble word!

Letter values in Scrabble US: P 3, I 1, N 1.

Is it a valid word?

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

a piece of jewelry that is pinned onto the wearer's garment
when a wrestler's shoulders are forced to the mat
small markers inserted into a surface to mark scores or define locations etc.
a number you choose and use to gain access to various accounts
informal terms for the leg
axis consisting of a short shaft that supports something that turns
cylindrical tumblers consisting of two parts that are held in place by springs; when they are aligned with a key the bolt can be thrown
flagpole used to mark the position of the hole on a golf green
a small slender (often pointed) piece of wood or metal used to support or fasten or attach things
a holder attached to the gunwale of a boat that holds the oar in place and acts as a fulcrum for rowing
a club-shaped wooden object used in bowling; set up in triangular groups of ten as the target

Also: personal identification number, pin number, pin tumbler, bowling pin.

Not playable in Scrabble US: IMMOBILISE.