I think the "Slower Traffic Keep Right" signs may encourage noncompliance because nobody wants to think of themselves as "Slower." Perhaps a better sign would be "If a car passes you on the right, YOU get the ticket."
Alternatively, "keep left lane open for passing", which I have seen on overhead electronic signs on 400-series freeways in Ontario.
Marines notwithstanding, people tend to be okay with being slower in the high desert area of Southern California.