Not my opinion, this is from the Bible...look up 1 Peter 3:3-4
Personally I dont wear any jewellery. I find its annoying. Even when people give to me I dont wear it. Also its easy to lose! Probably thats why I dont wear it, but just dont like the feeling of having stuff around my neck, unless its a nice warm scarf on a cold day.
It looks nice on others but I dont really put much stock in whether others wear jewellery or not.
Having said that the clay crosses do look nice and maybe they would make a good gift for someone who likes wearing jewellery, but many people that wear crosses may not be aware of how deep faith goes, its not just on the surface. Non believers wear crosses too, and others get tattoos, but God looks on the heart.
As for being a symbol of faith, yes its an important symbol which is why most graveyards have crosses, to signify hope in the resurrection. I notice that people that get cremated do not have such symbols at their resting or burial site, even many do not even get buried at all.