Television channels market themselves in a variety of ways:
The second series of Sherlock ended on a cliffhanger, with the question posed: is Sherlock dead? The first teaser trailer for the new third series saw the BBC market the show in a very creative way.
In the trailer we see a room full of young people who all look at their mobile phones after receiving the same notification alert.
They have been notified that Sherlock is alive.
A series of hashtags about Sherlock still being alive then flood the screen, and the trailer ends with the hashtag #sherlocklives.
After this trailer was broadcast, excited fans took to Twitter using the hashtag suggested by the BBC trailer.
The trailer was also available on YouTube and was shared on social media with the trailer and the hashtag trending worldwide.
Television programmes can be exported globally as a television format. Shows like Big Brother or Strictly Come Dancing that have a formulaic structure are easily adapted by different countries.
Strictly Come Dancing's format has a global appeal
The programme is known around the world, in its international format, as Dancing with the Stars.
It is estimated that 250 million people have watched these various national versions of Strictly Come Dancing, showing the format's global appeal and marketability.