I've been thinking about email signatures quite a bit recently, and especially what I'm supposed to understand by the terms you've chosen to use
"Sent from my iPad/iPhone" - I have a shiny apple product and haven't changed the default signature
"Sent from my android tablet" - I have an android device, and haven't changed the default signature
"Sent from my iPhone. Message may be short." - I have a shiny apple product and am letting you know that as a consequence of me using this device, my message may be short
"Sent from my phone, so may be terse" - I have a phone (not telling you what kind, it doesn't really matter to you, the recipient), but as a result of using it, my message may be terse
At the moment I have no signature on emails sent via my phone. Mainly because I can't work out what I need you, as a receiver of my email, to know, if anything. Maybe, for the sake of hoping people give me the benefit of the doubt, it should read "Sent from my phone, it has a small keyboard, I sometimes hit the wrong characters, so apologies for any spelling mistakes"