Maybe everything on the island relates to Jack somehow.
There are a lot of hints that happenings on the island are subconsciously "inspired", and not just by Jack. For instance, the polar bear showing up after Walt read a comic book featuring a polar bear.
The test bunker is a good idea, but maybe it wasn't nuclear, maybe it was biological... maybe the quarantine sign was a reminder for people in the bunker to not go out into the test zone. And now that you mention it, the "smiley" could have been a command prompt....
spoilage done.