I think it is a Mexican weapon known as a "saca tripas" (gut ripper, or something like that). I believe they were derived from agricultural tools. IIRC, these were commonly used by Mexican bandidos in the late 1800s and, at one point, the Mexican government banned their possession.
Yours may well be an early version, as most I've seen had a spring on the inside of the grip that engaged with teeth that were incorporated in the blade, giving it a "flick knife" capability. Perhaps yours is an example of the agricultural version that led to the form. Your blade has a hole in it to accommodate a ring to which was added a leather thong. The thong would be used to secure the weapon to the wearer's waist belt. The version shown below has the hole in the short arm of the spring instead of in the blade. It is etched with the classic Spanish warning: Si esta vibora te pica' no hay remedio en la botica
(if this viper bites you, there's no remedy in the pharmacy). The carved detail at the end of the grip supposedly represents the head of a viper.
Here's some more detail on the history: http://savatedansederue.com/history...ca-tripas-knife