Both things are possible and are done around here. With an environmental effect you just need to take care that it's subtle and not excessively shiny in dark interiors.The highlight is indeed pretty weak, but that's because I have some doubts as to if to use the environment effect instead or no. There are reflection textures in the PC data, so I take it using these would be okay?
On the stamp designs I can't help you much. For the colovian tomb urns I have used some celtic knot patterns. Maybe Oak sprig - patterns? Maybe a lionhead ornament taken from textures.org or somewhere, refashioned to show a tiger head instead? The outlines of a tower with battlements? Alternatively, abstract patterns like lines or dots could work.
If you intend to make them similar blocky as the rings are, they should be make armor bracers. We already have the colovian hats, so it shouldn't be a stretch to look for these among the armor objects.Now that I think of it, there was another jewelry item type I wanted to ask about - the bracelets. They could be implemented as armor bracers, like the Slave Bracers in Morrowind are. I'm asking it mainly because they could use designs similar to those of the rings.
Edit: Jiub, can we have those or similar coins for the Colovian tombs, too?