I personally do see the point in having names on your back. What if you're walking towards someone who's facing the other way and you want to introduce yourself or say hi?
Peg's idea is good but doesn't seem to hold much relevance to the location (just my 2p
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I'm also with dizzy saying that the text should be on the outside of the disk. A colour that's easier to see on black would be nicer too, like white text? If it was on white tshirts then the text could be black?