Have not been able to confirm this, but I think that mark was used by Manoah Rhodes & Sons Ltd.
Manoah Rhodes was founded in Bradford Yorkshire in 1836.
Thomas Ackroyed Rhodes was made managing director in 1888.
They had a sterling MR (in conjoined circles) mark entered in Sheffield and London.
The firm also had an AR sterling mark (Ackroyd Rhodes ) entered in Sheffield and London.
I think your mark represents the letters AMR (Ackroyd Manoah Rhodes).


Pat.