Commuters are being issued with a checklist on how to spot potential terrorists at stations in London.
Passengers have been handed leaflets in which they are warned to look out for people using lots of mobile phones or being vague about where they are going.
The fliers were reportedly handed out to commuters at Waterloo during Thursday's morning rush hour.
They advise Londoners to call a confidential anti-terror hotline if they see suspicious behaviour, adding: "Don’t rely on others. If you suspect it, report it."
It comes as London remains on alert for possible lone wolf attacks in the wake of the Paris killings.
The six point checklist for things to look out for is: someone noticeable behaving differently for no obvious reason; someone with a large number of mobile phones for no obvious reason; someone with passports or other documents in different names for no obvious reason; someone who travels for long periods of time but is vague about where they’re going; someone buying or storing large amounts of chemicals for no obvious reason; someone taking an interest in security, like CCTV cameras, for no obvious reason.
Met Police chief Sir Bernard Hogan-Howe revealed today that the force is reviewing the number of armed officers in the wake of the Paris attacks.
A Scotland Yard spokesman said the leaflets are part of an ongoing effort to interact with the public and do not represent a change in approach.
