These were manufactured with block style rear sights in the same manner as most other Prussian style arms. The rear sights were dovetailed onto the breech plug tang, and it isn't particularly uncommon to find examples (usually Prussian M1809 Muskets) that have had the rear sights removed. Sometimes the mortise is filled, which is the case with the examples shown in this thread.
Ditto. The Prussians even added rear sights to Brown Bess Muskets and French ANIX Muskets that were acquired during the Napoleonic Wars. It wasn't until they began rifling their smoothbore muskets that the block type sights were removed and replaced with barrel mounted long range sights.
Well, Grayrock Volunteer, that's interesting info about the Germans/Prussians adding rear sights to foreign muskets they acquired - there has got to be some sort of German national characteristic demonstrated here!