Perplex City Postcard

So far the Perplex City postcard has been found in these locations:

Bologna Airport, Bologna, Italy
Chapel Hill, NC, USA
Cambridge, Cambs, England
New York Public Library, SE Fifth and 40th, New York
Abbey Road, London

Places searched:

Liverpool, Merseyside, England
Glasgow, Scotland
Manchester, England

Theories

The code below the Semacode means something. Working: Postcard Code
The PCPS maze may have meaning.
The PCPS maze is drawn by hand.
Postcard Discussion on Unfiction.

Content

Painting of Perplex City at night
The pattern of lit and unlit windows of the building in the foreground of the painting is binary for "helloworld"
Letter from Sente
Semacode pointing to Perplexcity.com (NOTE: Semacode is simply a Data Matrix ISO/IEC 16022 standard barcode containing a URL. You can decode semacode with any standard reader)
Code of 221545484848465100503215 - Postcard Code
A line "MC, Please expedite global release. S"
A stamp with a maze and "PCPS" in the centre
Text down the middle: "Despite heightened security Academy tours are still running twice daily from gatehouse twelve. Advance booking essential."
A full Perplex City Academy crest.

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