Yes, ink is a Scrabble word!
...and is worth 7 points in Scrabble, and 8 points in Words with Friends
ink
Verb
1. Append one's signature to
2. Mark, coat, cover, or stain with ink
3. Fill with ink
Noun
1. A liquid used for printing or writing or drawing
2. Dark protective fluid ejected into the water by cuttlefish and other cephalopods
What Scrabble words can I make with the letters in ink?
3 Letter Words
2 Letter Words