Justin Timberlake has been secretly signing copies of his autobiography.

The 'Cry Me A River' hitmaker released his memoir 'Hindsight: And All The Things I Can't See In Front Of Me' at the end of last month, and since then, he's been dropping into book stores at random and taking copies off the shelves to mark them with his signature.

On Wednesday, he took to Instagram and posted a third video of him sneaking into a store - this time Barnes & Noble at The Grove in Los Angeles - and signing a number of books.

He captioned the video: ''Strikes again. Come and get em, part III...(sic)''

The video followed previous similar posts shared by the 'Filthy' singer, having visited a different branch of Barnes & Noble two days after the book was released, and a Target store a few days later.

Among the revelations the 37-year-old singer made in his book was the fact he ''almost got expelled'' from school for smoking when he returned to Tennessee in 1994 after 'The All-New Mickey Mouse Club' was cancelled.

He recalled: ''I came home a lot more sophisticated and aware than I had been before the show, but I tried to downplay it because I just wanted to seem like everyone else.

''I became the class clown, disrupting class with my bits, not caring if the teachers were mad, only wanting to be accepted by the other kids.

''I started getting in trouble. I smoked pot for the first time. I got myself a can of tobacco and almost got expelled for that.''

Justin - who has three-year-old son Silas with wife Jessica Biel - also admitted he wasn't always well behaved during his stint on the Disney show as he and liked to team up to cause chaos.

He wrote: ''We had employee cards that gave us access to the theme parks for free.

''Ryan and I once stole a golf cart and drove it to the employee entrance for the Tower Of Terror. We went on that ride 12 times in a row.''