Well, now I saw the broadcast of this 60 Mintues segment and they had a section where the man who ran the local dump in which Pollack dumped his trash had scavenged a few of the canvases to make signs. One side was a "No Trespassing" sign, the other a partial Pollack rejected painting!
Could be a painting that Pollack wasn't happy with that got tossed but somehow didn't get burned or turned into a dump sign...