The poster at the London stadium shows Brown, Geri Halliwell, Mel Chisholm and Emma Bunton posing in outfits from their 2019 tour when they got back together - minus Victoria Beckham - to play a string of dates across the UK, including Wembley.
Alongside a picture of the mural posted to her Instagram on Saturday, Brown wrote "Wembley?? I'll say no more" and added a series of emojis.
Brown had previously revealed the girl group were "definitely doing something" this year after they marked the 30th anniversary of their first audition last month.
While promoting a new addition to her memoir Brutally Honest on ITV's Loose Women, Brown said: "We are definitely doing something... I'm probably going to get told off but I've said it, there we go! We are doing something this year."
The singer, also known as Mel B or Scary Spice, added that she was going to be "in trouble now" for revealing the news.
The pop group, who formed in 1994, went on to dominate the charts with hits such as Wannabe, Who Do You Think You Are? and Viva Forever.
In 2000, the Spice Girls entered a hiatus to concentrate on their solo careers.
Their 2019 tour was the first time the girl group had performed together since the 2012 London Olympics closing ceremony.
They have marked a number of milestones throughout the years including re-releasing their Spice album in 2022 to mark 25 years since its debut.
At the beginning of the year, a new set of stamps was announced by Royal Mail to mark 30 years of the group.
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