This policy applies to MaineDOT electronic signs/boards or contractors working for DOT on all State and State Aid roads. However, it is highly recommended that any municipality using their own sign(s) on state or local roads be following the national MUTCD, specifically Section 1A.07 as linked here: http://mutcd.fhwa.dot.gov/pdfs/2003r1r2/ch1.pdf
This is the standard for ALL public roads in this country.
These Message Boards can only provide traffic-related alerts. There is a list of types of Unacceptable Messages such as advertising, public service announcements, greetings, such as " Welcome Home...", Town Meeting, Parade, etc.