A sponsor has been strategically placed on the shirt of every referee at the World Cup, with the logo remaining largely hidden until an official raises their arms.

In total, six billion people will engage with this summer's tournament in one way or another, according to FIFA, while more than five million fans are expected to attend matches across the United States, Mexico and Canada.

FIFA's expanded tournament is guaranteed to get airtime, so Rexona's decision to deliver one of the most strategic sponsorship placements in World Cup history could prove to be a masterstroke.

As seen in the picture below, the Deodorant brand's logo is positioned directly under the armpits of every referee's shirt, meaning the logo is hidden for the majority of the game.

But when an official decides to make an important decision, such as awarding a penalty, issuing a card, or holding up the electronic substitution board, the Rexona logo is clearly visible to those watching at home.

Rexona, known as Sure in the UK, also has its logo stuck on the substitution board, but the deodorant product being advertised under the armpit has been applauded by many.

The Activation, a page on LinkedIn, celebrated the sponsor.

"Someone had an idea. Put the logo on the fourth official's jersey too. Right in the armpit area. So every time a substitution happens, the board goes up, both arms raise, and the Rexona logo sits exactly where a deodorant logo should be," they wrote.

"Right under the arms. On the biggest stage in football. In front of six billion people. It only works because of the action. The board going up is the trigger. The arms raise. The placement clicks."

They added: "You see it and you laugh because it is so obvious and so perfectly timed that you cannot believe nobody did it before."

Why so many players are wearing pink boots at World Cup explained

It didn't take long for viewers to quickly notice in the opening moments of Mexico's win over South Africa last week that most players appeared to be wearing the same footwear.

It is a trend that has continued across the tournament, with just about every World Cup group stage match so far dominated by the bright choice of footwear. But why?

This summer, it just so happens that all of Nike, Adidas and Puma opted for pink as their main design colour, after Nike research claimed that athletes feel most confident when they are wearing bright, bold boots.

“What we’ve been hearing consistently from the athlete and the consumer, especially when it comes to big moments, is that bright colours give them confidence, so that was really our starting point,” Odinga Nimako, a senior figure at Nike’s global football footwear team, told The Athletic.

“The way we approached it was focusing on what are some of the brightest colours, what are those colours that are really amplifying that confidence, and pink is one of those colours.

“What we always hear from our consumers and athletes is when you wear a colour like pink that is so loud and so bright, it is like… You need to be really good to wear these (colours) as well. At the same time, there’s also been a level of acceptance with pink that makes it not too niche for people; it speaks to a broad audience.”

Another key factor is that bright pink quite clearly stands out. Not only does the colour tone contrast well against the green pitches, but none of the 48 teams at the World Cup is wearing a pink kit.