B of course.
This is the Aircraft ID. You can not mix it! No matter on which side, you must read the letters and numbers in exactly same order. Imagine, how confusing would be, if the aircraft ID will be different on the two sides (and the bottom surface of the wing).
There is plenty of 110 photo, not the same planes, but you will notice the rule of the markings:
http://www.asisbiz.com/Bf-110.html
Photo was made from both side:
http://www.asisbiz.com/il2/Bf-110/Bf...)-Habisch.html
http://www.asisbiz.com/il2/Bf-110/Bf...2-(5F+YK).html
http://www.asisbiz.com/il2/Bf-110/Bf...CM)-Runde.html