Marker of the Beast

In the future, we’ll all have barcodes tattooed on our foreheads, but until then, it would be very helpful if Google Glass could recognise your friends (or enemies) by some kind of visual code that doesn’t look quite so apocalyptic. Your task is to create some kind of unique visual ID that can be applied to a face localised within an image, giving feedback to the Glass wearer such as what bands or sports teams you follow, what kind of beer they should buy you, or so on. The Viola-Jones face tracker can identify faces within an image, so from this starting point, you should work out what kind of coloured dots, stripes, or other decorations would uniquely identify any person in (say) your College.