LONDON, England (CNN) -- Having a gun pulled on you in Sao Paulo would be a frightening prospect if you weren't walking the streets with Iron Maiden guitarist Janick Gers, and the gun-wielder wasn't an autograph-hunter... oh, and a policeman.

"I'm a cop," says the man, laughing and revealing a pistol.

Seconds earlier, he'd pulled up besides Gers and the Revealed production team in an unmarked car in a back street of Brazil's most populous -- and dangerous -- city.

"I want a picture. I am police."

After rummaging through his bag for his identity card, the presumably off-duty policeman produced a red leather biker vest which Gers duly signed in blue biro. The excited fan shook his hero's hand.

"He'll be arresting people at the concert," Gers laughs.

This is what life is like for Iron Maiden in South America, a hotbed of Maiden fanaticism.

"In South America, it's like verging on hysteria," says Adrian Smith, one of the group's three guitarists.