A year and a bit ago, I spent a semester studying mathematics in Moscow. Much to my surprise, rather than using the standard glyph "σ" to denote the Greek letter sigma, people invariably wrote a backwards delta "δ" (that's to say, with the top tail pointing to the left rather than to the right).
Does anybody have any insight as to the origins of this practice? I have been unable to discover anything about it. My best guess is that the tail of the regular "σ" somehow got curved upwards and then back over time.
Edit: I've attached an illustration of what I meant by "backwards" delta. The glyphs for "Russian sigma" and "Greek delta" are distinguishable: they're mirror images of each other. Moreover, I observed this peculiar style of σ from several faculty at the university.