A...…Book? Any ideas?

[Philip.S]

Gentlemen,

 

After dusting off some of my shelf, i thought that my Sztahanovista's case seemed oddly heavy, compared to other, similar ones. 

A while ago, a forum member showed a document that they had found under the felt inlay of the case of an excellent worker medal.

 

You, can, I'm sure, guess what I did; I gently pulled out the felt (It wasn't glued in, and I didn't break anything, I promise!), and, lo and behold, There was indeed something lying in there!

I took it out, and, seeing the letters: "S" "Z" and "T" (I assume), I hoped it was a document, just a folded over one, which would explain the abnormal weight!

Alas, upon turning it over, I was met with blank card. It appears to be a cut up piece of a book cover

 

If anyone has an idea as to what the poor, sliced, book once was, please do tell me!

 

I the meantime, has anyone else had such encounters with mysterious (or not so) stowaways lurking in your cases?

 

 

Many Thanks,

 

Philip.S