A recent discussion on the roadgeek yahoo group yielded the appearance of a blue stop sign. Yes, blue. Not yellow, not red, but blue.
This oddity was spotted in a parking lot in Hawaii and was explained that signs on private property (such as parking lots) can be any color except MUTCD standard (in this case, red). Seems to me like someone has misinterpreted the guidelines.
The actual sign and the story behind it can be found here.
It is reported that a proposed change to the MUTCD will eliminate any confusion and specify that all signs must conform to federal standards, including ones on private property. I wonder if that will affect the non-standard Interstate 55 sign I saw in Illinois a few years back?