I'm amazed at how often I see Delta everywhere. There are Delta Growers (fresh green beans etc) the Delta Queen paddle steamer on the Waikato river, Delta Transport etc. It seems a popular letter for some reason. You don't see mu, iota or epsilon used much.
That would be because in several of these references, if not all of them they refer not to a letter but a geographical feature-- i.e. where a river spreads out forming a delta... which a paddle streamer would naturally travel through, agriculture is often found, etc. I do believe this is derived from the letter d delta, which was a triangular shape, because the river makes triangular shapes at its delta. But the Delta Queen was not named as the fourth in its series after the Alpha Queen etc.
Or am I missing the fact that you were joking?