I was just wondering how, observationally, we would distinguish a distant galaxy of "normal" matter from one of antimatter. Maybe there is a simple answer but I don't see it. Once I started thinking about it, it bothered me. I will often come across an article that says (paraphrasing) cosmologists can't account for asymmetry in matter/antimatter in the observable universe.

What technique do they use to distinguish the two remotely? Suns and "antisuns" would have the same spectra as would all the elements and their counterparts so far as I can tell. They have the same masses, so gravitationally they wouldn't be distinguishable. Am I missing something?