Strange occurances

Found the following on my screen when I reported to my desk this morning
I have our top decoders trying to crack this. The image was up on the front page
I'm thinking it was a prank by the janitor. but my computer is locked down and only my key card can decode it.
When I went to my email however I discovered
that my email was swarmed with spam email all of which contained images with strange symbols like the images at the bottom of this.