It is easy to find examples of police enforcing made-up laws. Here is an example from the Department of Homeland Security:
"There are certain things that the press cannot do when it comes to national security, and filming federal buildings is one of them," said Luis Martinez, a spokesperson for the Dept. of Homeland Security.
This is a total crock. If it were true, no tourist would ever leave Washington DC -- they would all end up in jail. Via Carlos Miller, who is doing a great job blogging about the growing efforts by police to make public photography illegal. Mr. Miller, by the way, is still fighting in court against charges that he committed the ultimate no-no (as far as police are concerned) -- photographing a police officer in public.
Police have decided that the way to avoid having problems like the Rodney King beating which was caught on film is too.... prevent anyone from filming them! The police can fix just about any evidence, they will back each other up in even the most outrageous of stories, but the one thing they can't fix is video, so they want it banned. Lacking cooperation from legislatures in actually banning video, they have decided to ban it de facto if not de jure through their actions on the streets, hoping a cowed public will not question their actions.