Unknown Helmet Insignia

[Daremeister]

Hi team,

I recently acquired this helmet which has a red and dark blue diamond insignia painted on the side. I am not sure if this is normal but the diamond insignia seems to be impressed / branded into the helmet as opposed to simply painted on the outside. Can anyone assist with the unit flash identification and tell me whether it was normal to impress / brand unit flashes into the side of the helmets?

I should add that the helmet was picked up in Australia. Seller claims his father was a Royal Engineer. Stamped RO & CO Y***

Regards

DM