There are many candidates for the worst punctuation ever, but rarely is it actually dangerous. After the Second World War, Lord Haw-Haw, who had made propaganda broadcasts for the Nazis, was hanged because of a comma, or so the story goes.
However, the Metropolitan Police have managed to plumb new depths with bad punctuation and produce advice that tells us to do the opposite of what they want us to do and, if we were to follow what they actually wrote, we could end up getting killed. At the time of writing there are posters in London Underground stations informing us of what to do if we see an unattended package (a bag or something that has been left):
Don't touch, check with other passengers, inform station staff or dial 999.
Because they have used a comma after 'Don't touch', they say that we shouldn't touch it or ask passengers if it belongs to them. We should also not tell the station staff about it, nor should we call the emergency services.
In fact, they probably only mean that we shouldn't touch it, in case it's a bomb. They probably want us to ask passengers and inform staff, as well as letting the emergency services know. However, their advice is to do nothing.
Maybe the Metroplitan Police should check their punctuation unless they want people to be killed by their careless commas.