"Best" as a sign-off in a chat message

A new colleague of mine, a native English speaker with whom I have only communicated via text, used "Best!" at the end of a chat message.

1. Does this signify anything to the extent of "this conversation is over"? Is it rude to end a message like this without a lead-in?

2. Does the usage of "Best!" allow any educated guess at what particular brand of English said colleague speaks (British, US-American, Australian, and so on)?

I'm a native US English speaker who has lived for long periods in Europe. I have many friends and colleagues who are also native speakers of other varieties of English.

Based on my own experience, I can tell you that "Best" is very widely used in English-speaking countries around the world and in all types of online correspondence, whether email, chats, or other forms of social media.

I haven't often seen it used with an exclamation point, but there's nothing wrong with doing that. It's a question of personal style.

I would say that using "Best" is a widely accepted, friendly but not too friendly, polite way to end any type of written communication. And to answer your second question, I don't think it offers any clue about which variant of English the author speaks.

Merriam-Webster notes that closing expressions like "Best wishes" began to be shortened to "Best" around the 1930s, and it cites correspondence by F. Scott Fitzgerald as an example. It then offers this to say about "Best" as a closing: "Certainly, there are critics of this 4-letter, elliptical valediction; however, to most its simplicity crisply connotes a sense of goodwill without sounding stuffy or disingenuous."