Most Fridays, for about an hour in the early afternoon, I hold a "support our soldiers, bring them home now" sign in front of the federal building on the corner of "C" and 7th downtown Anchorage Alaska. This particular Friday was early afternoon late August or early September, 2012. The sky was completely overcast, little to no wind. The traffic on "C" runs south, and I was facing north holding my sign. Something moving caught my attention in the sky almost overhead and a bit to my left (west).It appeared to be a few hundred feet in the air, black or dark gray, and slowly heading in an arc south, then west, maybe 15 to 20 miles per hour. While it was moving forward slowly, it was pitching and yawing and bobbing in an almost violent manner, as if it were sailing on very turbulent ocean. I have never seen anything in the sky move in that manner so it is a bit hard to describe. It appeared to be roughly the size of a washing machine. In part because of its color and rapid movement, I could not identify its shape. The best I can do is that it was kind of like two or three balloons glued together with two or three pizza boxes in a random way.I kept staring at it trying to figure out what it was. I asked a couple of passers by if they could recognize it, but they could not. For a moment I thought it was some child's black helium-filled balloons that escaped, but the shape was too irregular for that, and it was not rising in the air, it was going on a fairly even horizontal plane. I thought maybe it was an eagle or raven, but when they fly by you can easily see wings, and this object had no wings, and did not move at all like any bird I have ever seen. It was too small to be an airplane, and in the wrong airspace, and was not shaped like a plane. I could hear no sound coming from the object. It did not appear to be a super big kite like are flown on the park strip because it was too compact, had no tail, and ultimately its total traveled path argues against that.I watched this object travel in an arc heading southwest until after 6 or 8 minutes it got maybe a mile and half or two miles away where I could hardly see it. Suddenly it stopped and hung for maybe a minute in the sky, and then started back pretty much along the same path, all the way back to where it was nearly over my head again at the corner of "C" and 7th. Then it suddenly disappeared. Maybe it went up into the cloud cover...I have no idea. It just disappeared. I have been looking for it, but I have not seen it since.