When discussing the minhag to give a ring the Ben Ish Chai brings down that it should be a silver ring with the letter “heh” engraved on the inside. This is speaking about the ring at the actual chuppah, not an engagement ring. I think he actually brings it down in last week’s parsha if you want to see on the inside.
I got my wife a ring like that for our wedding, but according to instructions I got from one of my rebbeim in yeshiva we also got it square shaped on the outside and circle on the inside (i guess square on the inside wouldn’t fit very well :p ). I’m not sure where he got that from but it looks very unique as I’m guessing most women don’t wear square rings.