Have you ever sat there scratching your head as you scroll through your Twitter feed wondering why some tweets start with a period before an @mention? This is one of those little known tricks that makes a big difference in who sees your tweets.
When you post a Tweet that is directed to someone by putting their @handle at the beginning it will only appear in the feed of that user and any common followers you both share. Did you know that? Twitter does this in order to cut down on the amount of Tweets showing in your stream when people are chatting back and forth with each other.
By putting a period BEFORE the @mention when starting a Tweet, your Tweet is no longer considered a direct conversation and will show up in the feed of everyone who follows you.
So, if you want all your followers to see a Tweet where you mention someone right at the beginning of your post, start it with a period.
It should be noted that this trick is only for when you begin a Tweet with an @mention. You do not need to put a period before the @mention when their handle is included anywhere else within the Tweet.