A comment by Phuzz, one the webpages comment section, says it well. You can even create spray paints in Counter-Strike which are images, these could be used to

A comment by Phuzz, one the webpages comment section, says it well. You can even create spray paints in Counter-Strike which are images, these could be used to hide secret messages. Point being, anyone can hide a message if they really wanted to without anyone noticing.