It's the I.R.63, which was named for Franz Josef I, but was granted the new Kaiser Karl's Namenszug after FJI's death. The official change date was November 3, 1917. By 1918 all units of the 12th Division were to wear a colored band across the bottom of their shoulder straps. The 63rd wore yellow, the I.R.23-red, Krankenträger Komp.Nr.15-green, etc.
The same Karl cypher was added to the Schulterschnur of the Husar Rgt.Nr.11.