Agreed. It seems that Caltrans does not want any signage for former routes that is no longer under their maintenance. But those should still be signed in some way, maybe as R routes, for relinquished.
We do need those routes for navigational purposes.
The local governments that take over relinquished route segments are usually required to maintain some signage to guide travelers to the continuation of the route, or some other part of the state highway system. But that requirement is often treated as a joke, and I'm not sure how it gets enforced.
The governments that don't treat that requirement as a joke often just keep up the old route markers for as long as they last. If you require them to replace the markers with "R" markers, the old markers may just disappear, never to be replaced. And does Caltrans even have authority to erect "R" markers on roads it no longer maintains?
There are too many unsigned/sparsely-signed routes in NorCal: SR51, SR77 (http://bit.ly/2Dj6X7J), SR112, SR123 (http://bit.ly/2EYRASs), SR185, SR222, SR262 (http://bit.ly/2mXE6zL), SR 283… I'm probably forgetting some. If you're gonna sign SR14U, sign them all.
The money for the 14U signs should go to signs for routes that make sense.
14U might just be a District 7 thing, or maybe shoving in Santa Clarita's face that the state really, really wants the city to take over that superseded part of old 14 (Los Angeles and Kern Counties took over the rest of the old route, which is now signed only as part of Historic US 6). Other Caltrans districts just remove the signage for the routes they want to remove from the state highway system (see below for examples), but for some reason not D7. At least one other U route doesn't have U signage, though the one I have in mind (8U across the river from Yuma AZ) is signed as part of an Interstate business loop.
As for some of the other routes mentioned:
51 is signed as part of Business I-80. The 51 designation keeps under state maintenance the part of old I-80 through Sacramento that isn't part of another route such as US 50.
222 used to serve a state hospital. The hospital has since been closed, and there is now a Buddhist religious facility on its grounds. Caltrans probably would like to give away that highway to the city of Ukiah, but maybe the city and/or the state legislature won't agree. In any case, it no longer belongs in the state highway system IMO, and the lack of signage (except on milemarkers and bridge identification markers) reflects its unimportance to the general public.
283 is a bridge, on a route otherwise relinquished to a local government that apparently doesn't want to pay for bridge maintenance. It is part of a (barely signed) US 101 business route. 275 is similar, the beautiful but expensive-to-maintain Tower Bridge over the Sacramento River, that Caltrans is having a harder time fobbing off on a local government than the rest of former 275 (which has no 275 signage, the state didn't require it).