It is anything but. Which is why vehicles, helmets and God knows what else are now marked with identification numbers, why they have sewn in numbers, etc.
If you see officers without numbers, go and find a senior officer (usually have orange or other coloured epaulettes on public order overalls), away from the current trouble, and make an official complaint. Repeat that formally later, including details of the senior officer and any action they took / didn't take. Accompany it with photographs.
I have to say that these allegations that officers routinely have no numbers do not accord at all with my recollection of disorder situations when I was serving and I cannot think that they have fallen back. There certainly were widespread instances from the 80s, but not more recently.