This exit sign on Interstate 5 shows the button-copy style that's becoming increasingly rare on California highways. Even rarer is the use of the style for US shields, since California has relatively few of those route designations.
In 2004, Caltrans appeared to have progressed well with its program to replace many older signs along Interstate 5 in Northern California with highly-reflective sign types which do not use button reflectors. This is one of two US 97 button-copy signs that I observed along Interstate 5 near Weed in September 2004.
This exit is also the southern endpoint of US 97, the major north-south route through eastern Oregon.