At the end of
http://www.vg-dreilaendereck.de/langendorf.htm , there
is a picture of a stone that might be DE2SNSTTH. It says that it used
to be the tripoint of Prussia, Saxony, and Thuringia. I don't think
the tripoint moved since then, but I'm not sure. The modern tripoint
definitely is in the neighbourhood of Langendorf. The stone is also
depicted in the coat-of-arms of this village.
Peter S.