I wanted to do a good job on the shields of my Athenian hoplite DBA army, the Xyston figures are probably the best on the market. I certainly wasn't going to attempt to paint them so that left decals.
You have two choices either conventional waterslide decals from VVV or the more tricky decals from Little Big Man Studios. In the end I choose the LBM decals as the VVV sheets are in a single colour meaning I would have to buy many more to get a reasonable selection, the LBM decals were just a single sheet.
The LBM decals are tricky, you cut them out, peel off the front clear plastic, place them on the shields, add a drop of water and after a couple of seconds the backing paper slides off.
Now as the shields are bigger than the decals getting them centered is a nightmare. Once on they can't be moved only scratched off so take care, and have lots of patience.
In the end hopefully they will look like the cover art on the box;