I just took a quick scan through Skennertonicon's "The Broad Arrow" and I couldn't find any R&HB marking for units under South Africa, or for that matter, any other country.

Here's a site provided by Amatikuluicon with some good information to bookmark for the future. I can't find that unit identifier there either.

Lee Enfield Rifle Markings (click here)

Regards,
Badger