Gold ring hallmark - mean?

by Richard O'Connor
(London, England (UK))

I have a gold ring with 5 hallmarks: (1)rect box with 3 letters - R&N, H&N, or the & could be a letter A , (2) Crown (in box) (3) number 375 (in box), (4) a single symbol(in box)- not decipherable and,(5) another single symbol(in box)- not decipherable

How can I find out what the hallmark means other than 9 carat gold indicated by 375 ?

Could you confirm if this is an antique hallmark