Copies of an old photo of pitcher Matt Cain, in his baby-faced years, and one of the Giants' most devoted fans have taken up prime space in the team's park. One has been taped to the wall of the team's batting cage, one in the clubhouse and another below the water jug in the dugout.

The fan in the picture, known to most of the team only as Billy, has been a fixture waiting to greet players and coaches at their parking lot for years. About a month ago, he vanished.

"Everybody's been worried about him," said manager Bruce Bochy, who chatted with Billy after most games and periodically provided tickets for him. "The fans who wait outside (to see players) have been asking about him."

His absence became conspicuous because Billy was always, always there for the Giants. He'd found a home in front of that parking lot, in more ways than one. A security guard stationed there, Orlando Green, offered him a place to stay whenever he wanted.

"You hate to see someone living on the street," Green said. "He could get mugged. He could get sick."

The arrangement began about five years ago, he said, and continued off and on until July 31. According to Green, Billy's last name is Chamberlain; he took medication to stay calm and received disability-based government assistance.

"I checked the hospitals," Green said. "I checked the jails. I even checked the morgue."

Other Giants employees, he said, told him that they had filed reports with the police. Green also tried, with no luck, to see if Amtrak had any information.

San Francisco police did not respond to messages seeking comment.

Billy apparently had found some places where he could stay in San Diego, Green said, and he'd travel by train and bus to Southern California to see Giants games. The team bus would pull up to Dodger Stadium, and he'd be there, waiting for them, usually because of a little collection taken up in the clubhouse.

Seeing him before games had become a ritual for everyone, even the team's writers. The Chronicle's Henry Schulman would get a Billy fist bump every day before home games. Bochy chatted with him constantly.

"We became friends," Bochy said. "He would wait for me after the games. It wouldn't matter how late I left here, Billy would be there. He'd say: 'I'm not going home till you come out.' And he'd be here when I walked in. Ninety percent of the time, he'd be here before I got here."

Green said Billy's cell phone went dead at the beginning of August. He had not cleared any of his belongings out of Green's home, and the security guard dug up the photo taken with Cain. Green couldn't explain why he felt comfortable opening his home to a man who was not related to him and who, as he recalled gently, needed reminders to bathe.

"It's a matter of trust," he said.

Green believes that Billy has relatives on the East Coast whom he never contacts anymore. He'd made another family out here, on the corner of Second and King streets.