The Garden State Parkway in NJ has the word "Parkway Entrance" on their iconic entrance ramp signs.
Someone mentioned on FB, the fact in the Northeast, a freeway entrance guide would be confusing as New York refers to its freeway's as expressways, which in actual definition is not a expressway, but something used commonly over time. Then the NY Parkways are another. Though many parkways in New York are indeed freeways, the Taconic and Saw Mill Parkways and the Westchester segment of the Bronx River Parkway are the real expressways as they are limited access with at grade intersections.
IMHO, I think the MUTCD should adopt this policy and have all states use them regardless of what people call them.