The set of three marks are hallmarks - they identify the purity of the metal and (at one time) the location of the assay office, or “hall”, where the quality of the gold was verified. I think you’re looking at British hallmarks, in which case the letter identifies the year in which the item was made. You can figure all that out with the link below. If it turns out not to be a British hallmark, you can also research the hallmarks of other countries that use that system from the same site.
How to read British Silver Hallmarks & Makers' Marks, Illustrated & Explained including the datemarks of England, Ireland & Scotland
www.925-1000.com
The F.C is the maker’s mark. The 925 site normally offers a link to their list of maker’s marks, bu it wasn’t working for me. Maybe it’ll work with your platform!
ETA: 925-1000 is a forum focused on sterling silver, but it might be useful to you since many jewelers work with both gold and silver.