If it is a Prussian potsdam the "Neisto" couls actually be "Niesse" one of the Prussian manufactories producing the M1809 (along with the Potsdam armory, where the common name for the arm comes from) The "Niesse" name has a Tall "S" that appears somewhat like an "f".

This is the main reason I asked if he could post a bit of a description a few weeks back :).