Thank you so much for taking the time to do a search. I bet you are correct, and I love your reference to it remaining a mystery like the Sphinx! Perhaps some checking on Farouk is my next step. It would be interesting to know how the cup ended up in a huge scrap yard in San Jose, California!
I hope you get to solve the mystery and tell us the results. It's still related to royalty because of the engraving implies it was presented to someone on his behalf. For now, think of finding what material is made of and search for how to clean it. Do not put it in a dishwasher, it has suffered enough humiliation already since the fall of Farouk.
Best advice is do an online search in your area of actual antique shops, and I mean the good ones with experts around, to give you a clue of what was this cup for.
You can also take pictures of all sides with your cell and go to a Reddit forum related to antiques and upload the pictures with the caption "can anyone tell me anything about this cup I found in my area...?" That flare will go around the planet and soon a person or more would recognize it and give you the story about it. If you solve the mystery on the initials, please tell us!
And most important, do NOT sell it! If is not that important make it your heirloom to pass to the next generation. If it's important, then check real auction houses for an evaluation and the percentage you get if sold. and I mean real auction houses, not the antique or pawn shop down the street.
Just think of this, in recent sports NY Yankees Aaron Judge hit two historical homeruns, the ball landed on a fan who was offered money right away. One fan gave the first one back to already millionaire Aaron Judge and just got presents signed from the Yankees, an industry worth billions.
The next one that got the other historical ball refused and kept it, and now will be part of a major auction. So, hope King Farouk, a legendary gambler and fan of horse races, brings you luck with that cup!