This past month I paid a visit to CA 189 between CA 18 and CA 173 in the San Bernardino Mountains. CA 189 is an interesting albeit short route at only 6 miles in length. What makes CA 189 fascinating is that it is signed with a route number which matches it's Pre-1964 Legislative Route (something it shares in common with CA 58 and CA 127). While CA 189 isn't signed from CA 18 nor CA 173 it actually has a pretty complete set of route signage which actually includes "end" placards at both terminus points.
https://www.gribblenation.org/2019/11/california-state-route-189.html