A London Tube sign that went viral, and was called a "wonderful tribute" by Prime Minister Theresa May was never found in any underground station in the British capital.

The sign said: "All terrorists are politely reminded that THIS IS LONDON. Whatever you do to us, we will drink tea, and jolly well carry on. Thank you".

It was created using an online tube sign generator, The Guardian reported.

The "sign" went viral online, and was read out by British MP Simon Hoare in Parliament on Thursday (March 23).

PM May said in response: "I think that is a wonderful tribute, and in a very simple way has encapsulated everything everyone in this House has said today."

Other MPs and journalists also shared the image of the fake sign online.

But not all signs being shared online are fake. There is a tradition of transport staff using London Tube signs to write encouraging messages.

The Tower Hill Station shared this message: "The flower that blooms in adversity is the rarest and most beautiful of all #Londonisopen #Westminster #WeAreNotAfraid"

It was shared on Facebook by Deputy Prime Minister Tharman Shanmugaratnam on Friday morning.

Khalid Masood, a British-born man, ploughed a car through a throng of pedestrians and then stabbed a policeman outside Britain's parliament on Wednesday.

The attack left five, including Masood, dead and injured about 40 people.