This is a clear violation of the First Amendment and should be fought in court. Picking and choosing what groups have access to government services in order to push a political agenda is not allowed. It is the very definition of tyranny.
Someone woke up The policy has been reversed. More Here
HOUSTON — Texas Department of Transportation officials in Houston are suspending the use of freeway message signs for firearms-related events, citing concerns about their use days after the Newtown, Conn., school shooting. “We had several people say 'Hey, this is bad timing,'” said Stuart Corder, director of transportation operations for TxDOT's Houston district. “We understand there is a wide a range of opinions, and we've got to be sensitive to people's concerns.”