The Cardiff Blues hooker is currently facing a spell away from the game as he receives extensive treatment for testicular cancer.
To show their support for Rees, who has played 58 times for his country, the squad asked for a personal graphic to be sewn onto each jersey for the game against Argentina this weekend.
Universally referred to as 'Smiler' the squad have created a purple smiley face to represent his nickname and chose the colour to show support for testicular cancer charities.
Wales captain Sam Warburton describes how the squad want to show their support for Matthew.
"After the South Africa game in the post-match function we spoke as a squad about how to show our support and recognise what Matthew is going through and we felt putting a symbol on the jersey would be good idea to show we are right behind him," he said.
"The idea was a purple smiley face. The purple to represent the testicular cancer charities and the smiley face to represent Matthew as we know him - Smiler.
"For me personally he has been a great support in my career and hopefully in a small way this shows how we feel."
Fellow front-row forward Gethin Jenkins, who wins his 100th cap for Wales on Saturday, added:
"Obviously Saturday will be a great day for me and my family personally but equally important is having the symbol on the jersey to show our support for Matthew and the tough times he is going through at the moment. We just want to show that the whole squad is behind him."