"legend has it was designed by a Civil War veteran who lost his arm. He fashioned the "hook" blade tip to allow the user to rake the tip on a belt loop or pocket and open the blade using only one arm. This is the ultimate display of a soldier adapting to any situation!"That odd crescent shaped tio functions as a sort of old school "wave" feature, allowing the blade to be opened one handed by hooking the tip on one's pocket. In a pinch, it works OK, but it requires some deliberate attention lest one's clothing gets sliced up.
This a quote from this link:
http://www.eknifeworks.com/webapp/eCommerce/product.jsp?Mode=Cat&Cat=159&SKU=RE18989
I have read of this before. that the "one armed" knife was invented by a verteran of the Civil War.