I now believe this wrench is fairly unidentifiable!
I think geneg has got it right. The logo on the wrench doesn't look like the "S" in a square but it may be the logo for the actual manufacturer of the wrench not Dayton-Symons-Superior.
I searched for Symons wrench on the internet but didn't come up with anything for this wrench but did find a similar tool (see picture) that I have listed as a What's Its in a couple of Wrenching News Auctions. It has also been in the Missouri Valley Wrench Club Newsletter at least once, submitted by a member unsuccessfully requesting information.
(http://i222.photobucket.com/albums/dd3/buswrench/message-board/Dayton-Superior-Wrench.jpg)
Here's a variation of wrenchmensch's wrench. It's 12.5" long and marked "Superior Nut Washer Wrench"
(http://i222.photobucket.com/albums/dd3/buswrench/message-board/Superior-Nut-Washer-Wrench-1.jpg)
(http://i222.photobucket.com/albums/dd3/buswrench/message-board/Superior-Nut-Washer-Wrench-2.jpg)