The policy of Aurora, Colorado went something like this ...
6" lettering - intersection of local streets.
9" lettering - intersection of local streets with major arterials.
12" (or larger) lettering - internally illuminated overhead signs at signalized intersections along major arterials.
Green signs - identified publicly maintained streets.
Blue signs - identified privately maintained streets.
All signs in Aurora, as was standard practice in the Denver metro area, always displayed the block number and direction ... of the street you were on, not the intersecting street identified on the sign. A bit bass ackwards, I know.
Denver used somewhat larger signs along major arterials to identify cross streets, with both uppercase and lowercase letters. On local streets, all signs were smaller, with all uppercase lettering.