Protective screens have been placed on the wall of Reading Prison adorned with the graffiti of street artist Banksy.
The picture shows a prisoner - possibly resembling famous inmate Oscar Wilde - escaping on a rope made of bedsheets tied to a typewriter.
The screens went up on Thursday, though the Ministry of Justice (MoJ) declined to comment on the activity at the site.
Rabble Theatre in Reading tweeted: "This is such a positive statement. At long last, our Banksy getting protected."
The Save Reading Gaol campaign group said it was "glad to see some sturdy protection" over the artwork "at last".
Still trying to prevent escape... 🤣 Glad to see some sturdy protection over the #Banksy #GraffitiArt at last. Here's hoping in the long run he will end up in safe hands... 🤞 #SaveReadingGaol#Rdg#Rdgnews#Banksystreetart #Createescape pic.twitter.com/YLl6lsL8Ep— Save Reading Gaol (@SaveReadingGaol) June 10, 2021
The typewriter on the mural was covered up and the words "Team Robbo" were added when it was previously damaged. Work has since been carried out to restore the artwork.
Robbo was a graffiti artist who died in 2014. He had been in a long-running feud with Banksy.
The incident led to campaigners calling for better protection of the artwork.
Reading Borough Council believes Banksy contributing his art to the prison suggests he is backing the campaign to save it.
Actress Kate Winslet, who is from Reading, told the BBC she believed the "incredible" wall art should remain and become part of the "legacy" of a new diverse cultural and arts hub.
But last month the MoJ rejected a £2.6m bid from the council to repurpose the derelict prison.
The MoJ said it would be put back on the market and it would "seek best value for taxpayers".
The sale to a developer of the Grade II-listed prison, where Wilde was held between 1895 and 1897 after his affair with Lord Alfred Douglas was exposed, fell through in November.
The jail was immortalised in Wilde's poem Ballad of Reading Gaol, which reflected on the brutality of the Victorian penal system.