letterboard

plural letterboards

1. A signboard for lettering or text.

   So reads the new slogan painted on the letterboards of New York City omnibuses.

   1941, Transit Journal: Volume 85

2. A board marked with letters of the alphabet, used for communication by the disabled.

   One of the patients, Leonard L., when he heard of L-DOPA, rapped on his letterboard with mixed enthusiasm and irony, 'Dopamine is Resurrectamine. Cotzias is the Chemical Messiah.'

   1973, Oliver Sacks, Awakenings

3. historicalmediaA board on which matter in type is placed for storage or manipulation.