zm, I almost always start a sentence with a cap unless the referent isn't upper case, such as "zm" or "tsu", though I might slip once in a while. As for final punctuation, this is a time-honored style, and if you flip through the pages of, e.g. a Time Mag, you will find many instances

You talking to me, Dahil? [Looks around the empty office.] You got the wrong referent. I believe it was tsuwm who mentioned the synchronicity of alarm at linguistic laziness and the stylistic lack of sentence final punctuation.

Ceci n'est pas un seing.