Sometimes I stumble upon the coolest knives! 

According the Official Price Guide to Collectors Knives, 15th Edition, the tang stamp: ULSTER (above) U.S.A. dates this knife ti 1941 – 1943.

I have this knife listed for sale on eBay if interested:
http://www.ebay.com/itm/1941-1943-RARE-HTF-Vintage-ULSTER-USA-Yellow-81Y-2-Blade-Jack-Knife-/200790030465?pt=Collectible_Knives&hash=item2ec004b881 

Enjoy the pics: