Comment There's always an exception to the rule (Score 4, Interesting) 272
"...there's no reason to have a certain sign on certain roads (Stop sign on an interstate highway)."
What about here? (Cross Island Parkway, New York USA, Exit 31)
Stop signs often do appear on highway entry ramps, especially where they are short. This is true in construction areas, as well as on some older entrance ramps around New York City.
Technically this is a 50 MPH (~80 km/h) Parkway and not an Interstate, but rather than randomly searching the area this was the first that came to mind.