SALT LAKE CITY — Red Voltage and two of his masked crime-fighting colleagues were approaching an intersection here in Utah’s capital on a recent evening, walking night patrol on foot, when a car suddenly slowed next to them. The night was bitterly cold, laced with a wispy stew of fog that might or might not conceal a thousand dangers. The car’s window rolled down.

“Hi, superheroes!” a woman shouted from within. “I’m in love with you guys!”

Eat your heart out, Batman. In a niche of urban life that has evolved in recent years somewhere between comic-book fantasy and the Boy Scout oath, a cadre of self-cast crusaders — some with capes, some without, all with something to prove — are on the march.

They prowl the night in Boston, in San Francisco, in Milwaukee, in Minneapolis, even as far away as Australia. Whether they are making the world safer or just weirder remains an open question.

Some go out armed with gear like mace, pepper spray or police batons; others say they carry only cellphones, aiming to be eyes and ears for the police, who in most cities, including Salt Lake City, are keeping a wary distance.