Hello New World !
Serbia and Bulgaria were not enemies during the First Balkan War : the siege of Adrianople was a Bulgarian victory thanks to the Serbian guns - and soldiers - which were sent there, and Adrianople woudn't have been a Bulgarian city, even for a very short time, without Serbia's help. You can see today at the National Military Museum of Belgrade the white flag of the Turkish general who preferred to surrender to the Serbians than to the Bulgarians. Here is a nice picture, too :
http://commons.wikimedia.org/wiki/File:Serbian_artilery_at_Adrianopoli.png?uselang=en
I have no idea about this medal bar, but it was possible for many Serbian soldiers to get Bulgarian Crosses for their bravery during this siege.
