In particular, that version of the WESTCOTT "S" pipe wrench is distinctive because the pipe grip is on the "fixed" jaw rather than the movable jaw, and because the pipe grip surface is a separate hard steel insert held on by the "wavy" base & screw. I had one in my "6 Inch Alphabet" display (
http://www.flickr.com/search/?w=27647617@N05&q=westcott ).
The more common WESTCOTT "S" handle pipe wrenches had the pipe grip on the movable jaw, so one wrench body could be switched from nut to pipe by swapping out the movable jaw.
The idea behind the "S" or offset handle was to gain clearance for your knuckles. They were introduced sometime in the last quarter of the 19th Century & produced until roughly mid-20th Century. WESTCOTT by Keystone Mfg. is perhaps the most common name but there are several others -- a few that come to mind include PERFECT HANDLE, ROBINSON, B&C, BULLOCK, the "Circle T" ones with the removable adjusting worm. One "S" prize is the B&C "S" combination nut & pipe wrench. (
http://www.flickr.com/photos/27647617@N05/8336544754/in/photolist-dGEYjf )
