I have been unable to find any maker of silver plated saddle trim with the initials HAG.
If you are able to remove the trim, I suggest you continue polishing with a mild silver polish. If your trim is lacquered you will need to us a solvent to remove the lacquer and then polish. Using a mild silver polish should allow you to polish for many years before wearing through the plating.
Re: Re: Silver Plate Saddle Silver- Maker Mark HAG
Thank you Fred, I appreciate the update. I did find out that the maker is Hansen Silver. I had another piece of horse equipment that I knew they had made; and when I removed the silver it had the same mark.