Indeed the town is easy to walk around quickly. Mostar still is quite a long bus ride away from Dubrovnik or Sarajevo so it's best to spend at least 2 nights there. I stayed for 3 and it was just right. Bosnia is pretty affordable as well
My explanaiton would be that the local football ultra group of Velež Mostar has a friendship with Trabzonspor and that they put it there. There is also a Galatasaray flag in Sarajevo old town, its from a restorant witch is called Galatasaray Čepapdžinica.
