Since Twitter began, if you’ve liked something that someone said, it has traditionally been seen as appropriate to Retweet. In the old days, Twitter Retweets included a customary “RT @Username” then pasting the Tweet.
A few months ago Twitter instituted its official Retweet function. Retweet confuses your timeline and shows up as an almost unnoticeable function-instead looks as if you’re following someone that you might not be. Further, Twitter's new Retweet removes the ability for you to comment inside of the Retweet. So, despite the official function, “RT” has lived on.
Twitter doesn’t seem to be too happy about that, though. It would appear that the site is, in fact, filtering out any Tweet containing the letters RT from searches.