I thought it was only illegal to HANG and LEAVE a banner above the freeway on the chain link fence, supposedly for safety reasons, in case wind blows it in into traffic etc.

I dont see how the cops can legally force the demonstrators to leave as long as they are HOLDING the banners and signs.

Bullies are cowards. Cowards dress alike and use force to intimidate people with less physical and/or legal power. This includes soldiers, cops and gang members.