Having discovered why the homunculus were gather 'sacrifices' Ed need to tell someone. The only problem was that Envy; one of the homunculus, was still chasing his target, Edward. Deciding that it was to dangerous to meet up with anyone, Ed drew a magic circle he created himself. This way no matter what happened to him the military would at least have the information they needed to develop a plan against the homunculus.
'Hopefully someone from the military would find the the magic circle and notice that something is wrong. Especially, Roy, he needs to figure out that something is wrong and figure out that the magic circle is created by me. It's obvious to those who know me, but it's completely unnoticeable to me enemy's.' Ed thought to himself.