http://www.perlmonks.org?node_id=29401

This code has the side effect of incrementing $A. It also increments /A on its PostScript side, though /A is defined to avoid PostScript undefined error.

/${1}def/#{def}def/;{/A}def/++{add}def/A 0 def ; $ A ++ # % Did you know my printer counted?
There are more than fifty ways to obfuscate $A++ documented at Paris.pm. Have a look!