I've tried te find some more information about the hallmark. According to the seller there is few difference between an 'A' and an 'R' so the hallmark can be 'P.I.R' from P.I Ronholdt, period 1893-1937. In the hallmarls listings on this website the date 1937 is common used. So I guess that the exact era is not always known ?
Can someone tell me if this designer or maker/silversmith has made this kind of jewelry ? It looks more from 'modernist' era to me..