G750: stands for 18K, where g is the initial letter of the word gold, 750 is the gold content, and 18K has a gold content of 750 (or 70%).

JJL 1: This should be the company code where you buy jewelry.

16#: This is a ring. Yes 16. Hehe, so is brother-in-law. Generally, men range from 15 to 18, and women range from 9 to 13.