Their fans of all ages embraced this gesture with a huge applause and naturally some screams - they are a boy band after all.
Their reaction means that when it comes to judging the show, they perhaps know best.
Friends Claire Farley and Kathryn Frame came all the way from Kirkcaldy to see the group they have supported for over a decade.
The girls have seen the boys live five times, and they first travelled to Wembley to see them perform in 1998.
Claire said: "It was amazing. You feel like you were entertained, it was real value for money."
Kathryn added: "I thought it was amazeballs. When they sang acapella, it showed how they have matured as a band.
"We have seen them through the years and watched how they have grown"
And there was no doubt that the girls were both excited to see a certain member of the band when asked who their favourite was, they both screamed, "Nick."
Friends Chelsea McIntyre and Zara Crawford, from Coatbridge, both pained their faces with a BSB sign - and Chelsea wrapped herself in a saltire flag which had I love Nick written all over it.
Chelsea said: "I have loved them since I was nine years old. I have never seen them before and I cried my eyes out as soon as they appeared."
Zara added: "In my head I wasn't bothered, I was just going with her. But then I downloaded their music again and started remembering all the songs.
"I loved it."
Janice Shaw, from Arbroath, admitted she is a Kevin fan, and added, "They look good for middle aged men."
Lisa Carroll, from Yoker, did not know what to expect as she had went to the show with a friend but she was pleasantly surprised.
She said: "I was with a super fan but I have to admit I enjoyed it. They are so good live and they have a great back catalogue of songs."
It's safe to say boyband mania has overtaken Glasgow yet again.
To read our review of the show including what we thought of support act All Saints, click here