A seemingly fairly rare motif is that of notes with heads on BOTH sides. The "head" side is almost always the obverse, with the reverse being reserved for other, non-portrait artwork. This thread is for basically, notes that seem like either side could be the "obverse" side, since both sides have similar portrait heads. First example is the Australian 100 dollar. The only way I can tell that the Lady side is the obverse is that the signatures are on that side. The Gentleman side could easily be the obverse too.