A tattooed sheath is a definite possibility-----but-------The preparation takes time, a lot of time! One of the horrors of world war 2 was the unveiling of some of the atrocities that had been subjected to some of the victims. One that I remember vividly was seeing lamp shades made of tanned human skin that had been tattooed . The results were gruesome in nature but artistic in design.
I believe that if a cow were tattooed in the design you desired, that it were allowed to heal, the cow be slaughtered, the hide tanned etc---that a sheath could be fashioned as you want. I rather imagine that a sheath of this nature would be cost exorbitant---------------but different!!! Sandy