Austria Cancel Question

I have a small fledgling collection of early Austrian stamps (I like the designs) and picked up a couple at stamp club tonight. Admittedly I've done little research on these, and I probably paid too much for this one because I'm pretty sure it is a #24, but was wrongly ID'd as a more valuable #19.
Regardless, it's mine now. Once I got it home and really looked at it, found the cancel curious.
Take a look...



...and sideways for a better look at the cancel.



Any ideas where it may be from or what the No. 4 refers too?

You have a traveling post office cancel. The full cancel reads

K.K. FAHRENDES
POSTAMT No. 4

The 4 is the route number, and the K.K. is the same Kaiserlich Koniglich that you often see in relation to Austria, roughly translated to 'imperial and royal'.

Interesting piece.

Hey, thanks for the info Cjd. That does make it more interesting. Will make a special note on its tag (The Austria collection is housed in Vario pages and each stamp or group gets a tag).