Last Saturday (5 October), Harry Styles sent Twitter into meltdown after writing just two letters: "Do".

Yesterday (9 October), a number of posters and billboards have been spotted with the writing: "Do You Know Who You Are?"

The posters have a Columbia Records logo on it, and also the acronym "TPWK", which many fans believe stands for "Treat People With Kindness", a phrase that Styles has used many times.

It's already been two years since Styles released his self-titled debut album.

Back in August Styles revealed that his second album is about "having sex and feeling sad", and added that he did "a lot of mushrooms" while in Malibu's Shangri-La studios.

There's no confirmation if the posters are linked to Harry Styles as of yet.