Most people have made fanart for the situation such as Reapersun has. Reapersun / Via reapersun.tumblr.com
There are a variety of posters that have been made about the fandom’s movement.
Fans all over the world in places like Lithuania, Milan, London(obviously), Japan, and all over the street lamps, crosswalks, and schools in America. Via moriartysliveinchum.tumblr.com
Most people have also taken up the liberty to buy, produce, or make their own stickers to spread the movement in places like the Burger King that this was placed in.
I’m guessing you could consider this harmless vandalism. Via cantorii.tumblr.com
Someone in the original poster’s school has taken up the chance to vandalise a wall with the hashtag. Via otakulord89.tumblr.com
A group of people have put up posters(that had to be taken down) at the London flat where they film the show. Via bakerstreetbabes.tumblr.com
The Sherlock fandom is probably most involved on the internet, but a lot of people are happy to see that it’s been integrated into the real world. As far as we know, the creators or actors involved with Sherlock have no idea what’s going on.