All the Police helmets I've seen have been painted Police blue,so this might be why you do not recognise the lettering. I'm not saying the helmet is wrong, it's just not the norm, the letters do look old.
It might have been used by one of the Police reserves.
As always thank you, Aaron!
Hi Roberto, the lettering appears to be on top of the corrosion to me? Personally I would wait for a standard example, they are not uncommon. Leon.
"Always do sober what you said you'd do drunk. That will teach you to keep your mouth shut." Ernest Hemingway
Thanks Leon, for the advice.