I have a set of (appear to be modern) pierced earrings. They are hallmarked 750, which I know is 18k gold. There are other hallmarks that include a sun in one stamp, a three-leaf clover in another stamp which contains two "C"s, a "G" and what looks like a tower of some sort. There is another hallmark which contains two "C"s and a (maybe) maltese cross. I have researched the internet for hours to no avail! Can you please help me? Just so you know, these are round, puffed, swirled earrings and each one is about 3/4" x 3/4". Thank you SO MUCH in advance!

This isn't really helpful at all, but it might be a personal artist's stamp. Using the initials and forming a symbol is extremely common.

Good luck!