I was in the awards and engraving business for over 40 years. I've engraved hundreds of guns over the years, but most were common, like Ruger Blackhawks. If a customer wanted a gun with any collector value engraved, I usually advised against it. I did most of the engraving on guns in my city, because word got around that I was a "gun guy" and wouldn't freak out if someone carried a (boxed) gun into my shop.
I once engraved a Winchester for King Hussein of Jordan and a 1911 for his son, the prince (Hasan , I think). A couple of foreign students at our college bought them as gifts for them as a thank you for sending them to college.