@mmn @andstatus, years later, K-9 Mail's mildly self-deprecating default .signature finally enlightened me: "Sent from my Android device with K-9 Mail. Please excuse my brevity". It's basically saying "Sorry if this message sucks, I had to send it with sucky software"—I like that; I would have immediately understood if the iPhone added something like *that* to its users' messages.