That shirt is a metaphorical representation of Perl's visual style.
Guido van Rossum would wear this shirt: http://1.bp.blogspot.com/_zqFoq3qej2c/SJM4eDsnzII/AAAAAAAAR8...
Guido van Rossum would wear this shirt: http://1.bp.blogspot.com/_zqFoq3qej2c/SJM4eDsnzII/AAAAAAAAR8...