"It belongs in a museum!"

That strange Indiana Jones journal that arrived at the University of Chicago?

Turns out it was Old Man Withers... no, wait.  Sorry, wrong mystery.

They did figure it out though:

For those of you who have wondered as hard as we have how we came to get this Indiana Jones journal: we have our solution.

You will have to RTWT to get the interesting details.  Note that the bit about the Egyptian stamps being honored by the post office may seem odd, but is entirely plausible.