Arguably the most popular human expression is being "booked". The latest version of the "smile-drifting" book will set off on a new journey from the northeastern Chinese city of Shenyang to mark the upcoming World Smile Day on May 8 this year.

The smile-drifting book Hello Smile 4.0 is designed to fill blank pages with photos and messages about smiles that will be collected during the trip, said the organizer, Shenyang Broadcasting and Television Station.

Starting from Shenyang in 2012, the first smile-drifting book has travelled through China and dozens of countries and regions.

The World Smile Day was launched by World Mental Health Organization in 1948 and is the only festival celebrating human expression.

We are here in Shenyang, waiting for your smile, with our old sisters enjoying the sunshine. Kindly smile.

We are here in Shenyang, waiting for your smile, with our incoming baby. it is our first family portrait. Happy smile.

We are here in Shenyang, waiting for your smile, wandering in the book store with her. Sweet smile.

(Photos provided by the organizer)