Apparently the punctuation mark indicates anger. From The New Republic:
This is an unlikely heel turn in linguistics. In most written language, the period is a neutral way to mark a pause or complete a thought; but digital communications are turning it into something more aggressive.
“Not long ago, my 17-year-old son noted that many of my texts to him seemed excessively assertive or even harsh, because I routinely used a period at the end,” Mark Liberman, a professor of linguistics at the University of Pennsylvania, told me by email. How and why did the period get so pissed off?
It might be feeling rejected. On text and instant message, punctuation marks have largely been replaced by the line break. I am much more likely to type two separate messages without punctuation:. . . .
“The unpunctuated, un-ended sentence is incredibly addicting,” said Choire Sicha, editor of the Awl. “I feel liberated to make statements without that emphasis, and like I'm continuing the conversation, even when I'm definitely not.”
Other people probably just find line breaks more efficient. An American University study of college students’ texting and instant messaging habits found they only used sentence-final punctuation 39 percent of the time in texts and 45 percent of the time in online chats. The percentages were even lower for “transmission-final punctuation”: 29 percent for texts and 35 percent for IMs. The same is likely true of Twitter, where the 140-character limit has made most punctuation seem dispensable.