It is a streetlight minus the supporting gooseneck support. Enlarge the photo and you can easily see an identical light diagonally across the street on the pole with another red light on it. The light is on a visible gooseneck branching out to the right over the street. Notice the branch begins just under the rectangular sign about a foot below it. Then look at the right hand pole top. You will see the beginning of the missing branch support just below the apparent top of the pole which "ends" exactly at the top of the background building. Too easy. Come on guys, Seattle would not put up a pole with with just unused braces at the top. The gooseneck and pole top have been removed.