Well, like at my school, most of the time when there is a wet floor sign placed right in the middle of the doorway, there is also a cleaning cart there and a cleaning person inside, so it seems pretty clear that it's closed. And if the sign is by itself, but clearly blocking the walkway, I might think that meant "closed" too. (But I might sneak past because if they really meant "non-usable", they'd lock the door..) But no, if it's just a sign and it's not totally blocking the way, it doesn't look closed to me. Even if it's sort of blocking the way, I usually just think that's the part of the floor that's wet, and it happens to be near the door.
...So it ALWAYS means "closed"? Are you sure? D:
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"You gotta keep making decisions, even if they're wrong decisions, you know. If you don't make decisions, you're stuffed."
- Joe Simpson