|Our son is mildly autistic, and any itchiness to his clothes ups his frustration level pretty darn quick. But on some shirts, removing the tags made it difficult for him to tell front from back when dressing himself. At the same time, I'd made several simple shirts for myself that I was forever putting on backwards, since it was difficult to tell front from back on those, too.
Then, it hit me. Buttons ! A tiny one in the back would be easy to see, virtually unnoticeable to bare skin, and I had plenty that I'd recycled from wrecked shirts over the years. You could also use buttons to mark who owns what shirts, using color or size.
I also use the really tiny ones for doll clothes. Hope this helps someone !