Another form of qualifying "route signage" might be postmiles/mileposts used in California and Nevada, like this pair in Nevada at the border between Douglas County and independent Carson City:
http://www.alaskaroads.com/DouglasCoNV-CarsonCity-border-postmiles_DSC7713.jpgBoth signs are about waist-high, and identify the route (US 50) on which they are located. The Nevada signs are similar to California's postmiles.
There is at least one route already in the HB, near Wells NV, that appears to have nothing resembling route signage other than mileposts like those shown above at the Carson City line.
Some of California's unsigned state routes might also have regular postmiles, which I'll have to check out later. California's urban routes normally don't have postmiles. A more likely place to look would be something like CA 222 in Ukiah.
Lately, Nevada has been replacing mileposts on some routes with much larger versions, including mini-route markers, as here on NV 173 near Boulder City:
http://www.alaskaroads.com/NV173mm(CL)0-DSC_1972.jpgI've only seen the enlarged Nevada mileposts on routes also marked with conventional route markers, such as the one in the background of the above photo, next to the parked RV.