The sign didn't do anything by itself. Likely the cops were specifically dicks about the Triangle for whatever reason, probably because of the nearby apartments and civic interests.
It invariably comes down to a self-interest approach, if law enforcement really doesn't want the homeless there, they'll go elsewhere so they don't have their stuff thrown away, get jailed without drugs, etc.
But ultimately, Phoenix can't enforce anti-camping if the homeless have nowhere to go. From every legal and practical and ethical perspective, the current approach doesn't make sense. The court decision in LA was from 2006, but it is still *very* much in force.
Orange County just tried to pull off the same thing LA did 10 years ago and the story comes back the same.
Legally, it comes down to who will advocate for the homeless in Phoenix to raise the same Constitutional issue in a federal court: nobody, for now at least. So Phoenix Police, et al, will get away with it until someone comes around and raises issue.
But even without the federal courts saying no, Phoenix needs to get past using the police as a hammer because everything looks like a nail and instead make the shelter space available. To do otherwise is a colossal waste of time and resources and avoiding what's right. It is mind-bogglingly expensive but without the needed and due support from the federal government and no immediate solution to opioids, there's no choice in the matter.