It's almost certainly the item's "fineness". For most jewelry the gold's purity is measured in units of 1000, often but not always represented as a decimal, with 1.000 being pure gold. Thus 800 (or 0.800 or .800) would mean gold that's 80% pure, with the remaining 20% being other metals added to increase the alloy's hardness.
Not
An S inside a gold ring is the maker's stamp. If the ring were not gold and had an S inside it would stand for sterling silver.
the stamp shows that the ring is of 14 karat gold piece; to check if it is real or not.
What does it mean
GOLD SHELL = Equals fake or gold plate If the GS stamp is inside of a diamond shape it's the makers mark for Gottlieb & Sons.
Zinc coating(hot dipped) with iron n steel
14 carat gold
62.5 % gold
Gold electroplate. Not gold.
gold
what is GL stamp inside of the ring mean
The Stamp YAG Means Gold Coated Silver