In all honesty, the number looks like something someone penned on him. It very well could be a temporary tattoo done with henna. Now, if his 'roommate' says he had a tattoo, then obviously something is amiss with the photos.
There's so many wanting it to be a conspiracy, I could see photoshopping and making the tat transparent.
Just my thoughts...I assure you, there are more questions than answers at this point.
I can see the conspiracy-pundits having discussions on this for decades. It is their inner-yen for truth that keeps people from being too trusting of the dialog of msm.
Peace.