European 375 gold mark

It is a statement of purity. It means 375 parts per thousand or 37.5%. This is equivalent to 9K (karat).

There are three ways to indicate the purity of precious metals: 1) as parts per thousand, 2) as a percentage and 3) in karats with 24K being 100%. In the US and Canada, it is most common for the purity of gold and platinum to be shown in karats and for silver to be in parts per thousand.