Police identified the men after they shared a video online of them making the tattoo.

An online campaign has been created to help the boy get the tattoo removed.

The suspects, aged 27 and 29, confessed to writing the message, which said in Portuguese "I'm a thief and loser", as a "punishment".

Police in the city of Sao Bernardo do Campo, in Sao Paulo state, have not yet confirmed that the attempted robbery took place.

The boy said he had fallen over the bike for being "very drunk", but that he was not trying to steal it.

The two men caught the boy, tied his hands and feet and said they would tattoo him, he added.

"I asked them to make the tattoo on my arm but they said they would do it on my forehead and started laughing," he told Folha de S.Paulo newspaper (in Portuguese).

"I begged them to break my arms and legs instead."

In the video, the boy, who seemed frightened, is seated on a chair but not tied, while a man with a tattoo machine holds him by the hair. The man who is filming laughs and says: "It's going to hurt."

The boy also had his hair cut by the suspects after he tried to hide the tattoo.

The teenager's family said he had gone missing on 31 May and recognised him after seeing the video, which was uploaded on Friday. He was reunited with his family on Sunday.

The online campaign to help him has raised more than 19,000 reais ($5,800; £4,500).