Yes, signed is a Scrabble word!

Adjective

1. Having a handwritten signature

2. Used of the language of the deaf

Verb

1. Mark with one's signature; write one's name (on)

2. Approve and express assent, responsibility, or obligation

3. Be engaged by a written agreement

4. Engage by written agreement

5. Communicate silently and non-verbally by signals or signs

6. Place signs, as along a road

7. Communicate in sign language

8. Make the sign of the cross over someone in order to call on God for protection; consecrate