Placing a dot before Twitter Username sends Tweet to ALL Followers.
Below is a link to a post that explains why people sometimes place a dot before usernames when sending tweets:
Mystery Dot: The Best Kept Secret on Twitter
By Anneke Jong
August 31, 2012
If a tweet starts with a username, Twitter thinks it’s a conversation (or an @reply, in Twitter parlance). Twitter is pretty smart and doesn’t want to bother everyone who follows you with every personal conversation you have. You should be grateful for this feature if you follow any company accounts that reply to hundreds of user questions and comments per day.
To keep us all from being annoyed by tweets that are actually just conversations between people we don’t know, Twitter only pushes a “conversation” tweet to our feeds if we follow both the tweeter and the account mentioned at the beginning of the tweet.
You have to put something before the username to trick Twitter into thinking it’s a regular tweet for mass consumption. Perhaps you’ve seen people start their tweets with a period? Tricking Twitter is exactly what they’re doing.
If you haven’t seen this before, here’s a sample:
.@rachelsklar just took at the stage at #SXSW to talk about trends for women in comedy. Any questions I should ask her?
Now this tweet will get pushed to everyone following me, regardless of whether they also follow Rachel.