Blue Hawaiian Stop Signs

[Max Rockatansky]

I was discussing this item with another forum this morning, this is the explanation he sent me regarding Oahu:

But, as a general rule, highway billboards like what you see in other states are prohibited in Vermont (thankfully).  And, again, private persons cannot put up signs that are MUTCD-compliant or look similar to such.

Just on or near public roads (which is what I'd assume), or also on private property?  In Honolulu, there's an urban myth that a county ordinance says you can't erect signs on private property that match public road signs, which is why you see some blue stop signs out there.  County officials say that private signs conflicting with public ones are prohibited (such as a private Yield sign close to a public Stop sign), but it's OK for a non-conflicting private sign to be MUTCD-compliant.

That said, I did notice some Blue Stop Signs on my own visit to Oahu on places that would be considered public roads.  Most prominently there was a Blue Stop Sign on the departing tunnel leaving Diamond Head Crater.  There was also some Blue Stop Signs in Waikiki on the alleys which publicly accessible.  Does anyone have any idea why the blue variants would be present at those locations?