Signs like the one above are how St. John's deals with potholes in the short term, a technique I've not seen anywhere else. The hole in the picture is a particularly large one, but the sign and sandbag combination are the same around the city to mark holes. Eventually, after a few days to a few weeks, the signs are removed when some sort of fill gets put in the holes.
Personally, I find the signs worse than the holes, especially at night when they're hard to see (even with the orange stripes; they don't seem to be reflective). Every time I encounter one of these signs after dark, either parked cars, misty weather, or just plain poor lighting means I don't see it until I'm nearly on top of it, and I have to stop suddenly. I've come upon signs that have been knocked down, so I guess some people do end up bumping into them.