[finolex1]

In my experience this is pretty much a universal norm for all Americans below 30. Putting a period at the end of a sentence may come across as curt or rude.

Note: Rules are different for multi-sentence messages and single sentence messages. For messages with multiple sentences, its fine to insert periods between all sentences, but skip the last one. The above only applies to short messages with a single sentence.

[Jedd]

I know that historically, newspaper headlines were lengthier, and quite likely to be a grammatically valid sentence.

However, periods were never used to end them, as absent a period it invited the reader to actually engage with the rest of the story. (This story may be apocryphal, but it sounds reasonable.)

Perhaps there's a little of that going on with people's communications where they wish to imply there exists more than they are saying (which may or may not ultimately be delivered to the reader).

For my part - as an over-30 non-American - I'll stick with standard punctuation.