The distinctions between certain kinds of signs might not matter to the average customer, but when it comes to zoning laws and local regulations, the classification of your signage matters. Corrugated plastic signs are an option when other forms, like billboards, aren't, as one story from San Francisco shows us.
The SF Examiner reported on a decision made by the local government to police area businesses and prevent them from erecting billboards when they claim they are using "business signs." Although the measure currently approved by the city's Board of Supervisors is temporary, it does identify a dubious practice that could become the focus of more stringent rules later.
According to Supervisor Scott Weiner, who was quoted in the article, the problem stems from outdated guidelines that businesses are using to unlawfully manage billboards for other services and treat them like custom made signs. The line between the two is important to manage because of the role the signage plays in the community.
"Since 1965 business practices and advertising practices have changed quite a bit and we have seen some scenarios where a loophole has been identified by certain billboard companies where they have turned what are supposedly business signs into what are in effect billboards," he said.
One giant piece of building-side signage that has drawn complaints comes from the advocacy group BadIdeaCA, funded by a conservative agency. A bright yellow ad protesting a recent measure to raise the local minimum wage has been criticized by multiple news sources, including PandoDaily and Bustle.
That doesn't mean that you can't broadcast to a wide area. But consider using corrugated plastic signs and other more traditional and compliant pieces to avoid legal contention.