To embellish your sheath you'll need some tooling stamps. They're similar to a letter or number stamp. It's just a long metal rod with a pattern on one end. You get the leather slightly damp, place the stamp on the leather and strike it with a hammer. This will compress the leather, pushing the pattern on the end of the tooling stamp into the leather. The patterns available are nearly endless. You can do basket weaves in many sizes and patterns, or put some decorative pattern around the edges. Basically, you can put any pattern you want on the sheath.
I do the tooling first, so that the sheath is laying flat, as Mr. Adams suggested. I have a few that I made that I might put a border around the stitching only. That is the only place that is easy to tool afterwards.
Your sheath is very, very nice. Much better than my first efforts. I think you could probably do a border around the stitching on that one. It's would be very, very difficult to fill the entire side with a basket weave though.
Here is the first sheath that I tooled. Your sheath is similar in design to mine. I think that you could very easily put a border around the stitching. However, a basket weave, like I have on mine would be very difficult to do after the sheath is finished. You need to have the sheath flat and firmly backed to stamp in a pattern.
Tell me how to add some kind of pictures or pattern on the sheath leather?
I will think about making some tools for patterning.