OK, so I grew up in the Philly suburbs and watched Philly news always refer to downtown as "Center City". Yet, I never see a sign that says "Center City", just "Central Philadelphia". Is there a reason for this? Do they feel "Center City" is too unhelpful to the non-locals and "Center City Philadelphia" is too long for signs, so they adjust it to "Central Philadelphia" even though no one calls it that?
i wonder if it's because "Center City" could actually be mistaken as an actual city name.
The MUTCD often refers to names on big green signs as destinations. In that respect, they don't specify exactly what should be used as a destination, but rather state that it should be relevant to the motorist and consistent on signage when approaching an exit. Unincorporated towns, for example, are permitted, even though they're not official cities or towns. So, there's nothing that says "Center City" is prohibited; it would be up the transportation department to determine if it's good enough.