No Shoulder Numbers? No Authority!
When I was at school, many years ago, us boys were told that if we weren't wearing our ties, we weren't in school uniform. It didn't matter how much of the rest of the uniform we were wearing, it just didn't count without our ties.
It was a state school.
If a police officer is legitimately acting as a police officer, they will have no reason to conceal their shoulder numbers. "Nothing to hide..." and all that. So, when they're hiding their shoulder numbers, they're obviously not acting as a police officer. They're not truly in uniform, after all.
"But the man who assaulted me with that stick obviously wasn't a police officer!" the defendant will plead.
"The officer was clearly in uniform," the prosecution will assert.
"A real police officer would have had shoulder numbers. But this man, who was dressed like a police officer and trying to impersonate a police officer, had bits of gaffer tape where shoulder numbers would be. It was a dead give-away. That's how I knew he was an impostor!"
POLICE BE WARNED!
If you hide your numbers, you may be lawfully regarded not as police officers, but as criminals impersonating police officers. When you resort to physical force - or even threaten physical force - such action will be interpreted as criminal assault, which is exactly what it is. We will lawfully defend ourselves against such crimes, as is our right.
YOU HAVE BEEN WARNED
(Since I am only "threatening" to exercise lawfully held rights, this post cannot lawfully be construed as any kind of unlawful incitement, grounds for suspicion, or anything of the sort. I keep a copy of the European Convention on Human Rights on my desktop. So there.)