What is 753 on jewelry?

Answer 1

In Europe, gold is stamped with a three digit number to indicate the gold's purity. If you put a decimal after the second digit, you have the percent purity of the gold. (In your example, the 753 would be 75.3% purity.)

The European 999, or 99.9% purity gold, is equivalent to saying 24-karat gold.

The European 917, or 91.7% purity gold, is equivalent to saying 22-karat gold.

The European 750, or 75% purity gold, is equivalent to saying 18-karat gold.

While the number might be slightly off of 750, this is most likely the meaning of the 753 mark on gold jewelry. For a full list of common European/ karate comparisons, see the link below, where it is given in an article "Gold: 24 Karat or 999.