Perplex City Postcard

Jonas from the Unfiction forums picked up this postcard in Bologna Airport, and oneliiivewire got one from Chapel Hill, NC (Thank Jonas and oneliiivewire for the pics)

Speculation

The code below the Semacode means something.
The PCPS maze may have meaning.
Postcard Discussion on unFiction.

Content

Painting of Perplex City at night.
On the Image of the building on the painting, the windows convert to "helloworld" from binary.
Letter from Sente.
Semacode pointing to Perplex City
Code of 221545484848465100503215 - Postcard Code
A line "Mc, Please expetite global release. S"
A stamp with a maze and "PCPS" in the centre
Text down the middle: "Despite hightened security Academy tours are still running twice daily from gatehouse twelve. Advanced booking essential."
A full Perplex City Academy crest.

Letter on Postcard

My friends -

I need your help.
Cube - Missing.
Presumed Stolen.
Not enough room to 
explain here.
Too risky.
Your assistance will
be rewarded.
More contact to 
follow - stay alert.
Yours in hope,

Sente