Following the attack at Leytonstone station on Saturday night, in which the attacker is claimed to have shouted "this is for Syria" while slashing a man's neck, Londoner's have gathered around the hashtag #YouAintNoMuslimBruv.
Those words, which could be heard being shouted by another man who recorded footage of the alleged perpetrator as he was tackled by police, have been used to denounce the attack.
Since then the hashtag has trended on Twitter and subsequently an image began to be shared which appeared to show the words written on a sign at an unnamed London Underground station:
Lots of people have shared it:
And while TfL staff do occasionally write messages like this on the Underground:
This one is a big old fake:
Look, here's one we made ourselves:
You can make your own version here