Is "Sent from my iPhone" correctly punctuated and capitalized?

Solution 1:

The phrase Sent from my iPhone is a sentence fragment. It is capitalized, as other lonely sentence fragments are. I think of it as a "P.S." after a letter, telling the recipient from where the message was transmitted. The fact that it doesn't have a period matches this.

However, I don't think that it makes much of a difference how this phrase is capitalized or punctuated. It is used as a tagline at the end of messages, and it gets its point across as such.

Solution 2:

This is an example of the telegraphic style of writing. You see it a lot on signs, and this message is an advertising message, which is a kind of signage. You don't see periods on stop signs, do you?

Other signs: