It lets them send the tweet to all of their followers.
Any message you send beginning with @name is delivered to @name’s notifications (it also shows up in their timeline but they might not see it if they’re not online at the same time) and into the timelines (but not notifications) of anyone who’s following both you and @name.
While anyone can see any public tweet you sent by looking at your profile (if you’ve blocked them they can just log out by the way) no-one else will receive a copy of your tweet.
Any non-alphanumeric character before the @ disrupts the ‘addressing system’ and will deliver your tweet to all of your followers’ timelines. By convention the least visibly intrusive character is a full stop . but you can use , ‘ / etc. Numbers or letters won’t work because they also stop the @name from working (if it doesn’t show up as a blue clickable link it won’t go to their mentions).
You can also rewrite the tweet so that a word or phrase appears before the @name (in which case you don’t need the .).
Some confusion arises because the @name convention functions in three distinct ways
- as an addressing system to send a message to them
- as a denoter to say who has done something
- as an address to say that you are at a place
I could send these three tweets
- @barbicancentre I really enjoyed that event last night
- @barbicancentre will be screening this fantastic film tonight
- I am @barbicancentre
In the first I’m telling the Barbican Centre I’ve enjoyed an event of theirs. In the second I am (unsuccessfully) telling my followers that there’s a film on at the Barbican Centre (only BC and people following both me and BC will see it). In the third I’m clumsily announcing my location.
For the second example to work I’d need to use the . or rewrite the tweet, either of these would work:
- .@barbicancentre will be screening this fantastic film tonight
- I’ll be @barbicancentre for this fantastic film later
The strategy of . @ (“dot at”) is sometimes used to draw attention to someone else’s tweet, perhaps one that you disagree with. When using it in this way if you have a lot of followers, or you have ‘surfaced’ an otherwise hidden but slightly controversial tweet that others haven’t yet noticed, you might find that your followers ‘pile on’ to this other person and criticise them for their tweet. Just something to be aware of. A disproportionate ‘show of powe’r can come back to bite you.