Strange Cancellation/Overprint

[Feldmarschall]

Anyone recognize the strange overprint on these stamps?  I was able to use some software to make it stand out a little better, and I've recreated what it looks like for a little more legibility...I have yet to see anything about this in any of my catalogs and literature.  A friend remarked that he thinks it may be from some kind of a fiscal use, but doesn't know one way or the other and is basing that thought on other things he's seen from other countries.