blackboard
Use a combination of "black" and "square."
These days you will also see white-board and smart-board.
blackboard:
Sign: blackboard
Synonyms:
Handshape:
Right Hand:
Left Hand:
Location:
Orientation:
Movement:
Non-Manual Marker:
Interpretations:
Inflections:
American Sign Language University ™ ASL resources by Lifeprint.com © Dr. William Vicars