Vergnaghi is typical of the area of Milan and Lodigiano, Vernaghi, much much rarer, is always of Milanese, should derive from being the original families of a locality called Vernago or Vergnago, that is to be pertaining to the land of a certain Vernus, but It is also possible that it is instead of families from the north.
Buy a heraldic document with your coat of arms
Verba Volant, Scripta Manent