Just a wild thought, but there was a very prominent family in Jackson Parish named McBride. Since Jackson was a fairly new parish at that time (1845) it is remotely possible that there was a contingent that wanted it named McBride Parish, hence the flag inscription. I did note that there is a McBride Parish in Lincolnshire, England but it would even be more far-fetched that immigrants from there moved to Jackson Parish. The answer sometimes resides outside the box.