Hi the color of the stone in this ring is beautiful. There seems to be an awful lot of marks on this antique gold ring. A crown followed by 18 is the UK gold purity mark. 18K, 18ct or 750 (parts per 1000) or 75% gold.. Most quality pieces are 18K.
Not sure about the other crown mark, it doesn't sound like a UK country mark.
You might like to check the date letter which is the letter "S" against the date letters in the birmingham date letter chart. You can find the link "Researching British Hallmarks" in the Jewelry Resources.
Concerning the sponsor's mark you might like try contacting the The Birmingham assay office which is the largest assay office in the world.
