The sign over his locker says, "Think." The cartoon beside it, drawn in crayon by a child, shows Charlie Brown of Peanuts fame standing on his mound saying to his catcher, "How can I read your hand signals while you're eating cookies?"

The real-life catcher sags in front of his cubicle, almost too tired to remove his shin guards. He has won the game with a three-run homer off Jim Palmer. He has leaped three rows into the box seats to catch one foul ball and slid headfirst into a wall to catch another.

'I feel like a maple tree on the last day of March," 220-pound Carlton Fisk said to himself. "All tapped out."

Slowly, he unbuckled the shin guards. "Only 100 more games to go," he smiled.

The most indispensable weapon in the Boston Red Sox arsenal is hidden behind an iron mask. The brains behind the Over the Wall Gang wears the tools of ignorance.

Boston's Jim Rice is the acclaimed slugger, Carl Yastrzemski the classic captain. Fred Lynn means grace and Jerry Remy speed. Rick Burleson and Butch Hobson are throwbacks to the tough guys of yesteryear. Dwight Evans packs a .38-caliber arm and George (Boomer) Scott has a magnum force mouth.

But when the Boston gatling gun rolls into Baltimore today with its .699 winning percentage, Fisk, the patrician 30-year-old catcher who loves dirty work, will be the elastic holding up the Sox.

"Although Boston probably wouldn't fall apart without any one guy," says Baltimore Manager Earl Weaver, "the guy they'd hate to lose most, even more than Rice, is that Fisk.

"He does a lot of things for them, and every one of them is hard to replace."

Four Sox hit more home runs than Fisk's 26 last year. Two had more than his 102 runs batted in, and Rice surpassed his .315 average. But Fisk was voted the team's MVP, hands down.

Fisk brings glamor and grit, brains and brawn, to perhaps the most demanding and exhausting position in any sport.

Now, at the peak of his career, Fisk is the only total catcher in baseball. He hits for average and power. He leads the Sox in walks and runs scored. He is a huge, yet nimble receiver with a strong arm. No popup is safe from him. He delights in blocking pitches in the dirt, especially with men on third. ("One pitch got past me for a run last year," Fisk says with pride. "That's a statistic I believe in.")

Above all, when compared to the frequently injured Johnny Bench and Thurman Munson (both 30, too), Fisk catches a staggering 150 games a year.

In the last 10 days, as Boston has won six of eight games against New York and Baltimore, Fisk has been at his best, slugging .767 with 10 runs scored and nine RBIs. Almost every crucial, game-turning Boston rally has either been started or highlighted by Fisk.

Fisk has, in those eight games, made four spectacular catches of foul balls, forced two lead runners on aborted sacrifice bunts, been middle man on a bases-loaded doubleplay, tagged out two sliding runners and allowed just one stolen base.

Through these pressure days, Fisk also has been the Sox field leader and spokesman, calming the waters during Bill Lee's walkout, cracking jokes and lecturing the entire pitching staff on its sins.

"Fisk's out on the mound talking to the pitchers so much that I fall asleep," needled Lynn. "Without him, we'd play two-hour games. I've threatened to change the number of his position from "2" to "1 1/2."

Cajoling, babying and threatening pitchers is what Fisk does best.

Now Fisk loves every game. The combative Torrez is just his type. "Mike loves to be challenged, kicked in the butt," said Fisk. "I'm good at that."

Luis Tiant, however, needs an appeal to his pride, or balm for his ego.

"I'll tell him, 'The game's on the line right now, Old Man,'" Fisk said with a grin. "Time to light up your blankety-blank cigar and throw some fast balls."

Young Dennis Eckersley has learned, under Fisk's guidance, the beauty of changing speeds, while "Spaceman" Lee and Fisk are old cohorts in tormenting hitters with junk pitches.

Baseball is a total, intellectual passion for Fisk. He talks about the game incessantly, his conversation bristling with intelligence and humor. The Think sign is always in the background.

"My idea," he said proudly, "is really to play the game of baseball. Not many people know what that can mean. You don't give the other team a single extra out or base or at-bat. You don't even give them one extra swing."

That idea ruined the first five years of Fisk's big league career. The strapping New Hampshire lad risked any injury to rob a team of that one extra swing or not.

"Yeah, I've had to give that up," Fisk said disgustedly, chastened now by the broken knees and arms of his youth. "When in doubt, preserve the body. I don't block the plate anymore, I admit it.I'm the master of the 'ole' tag."

Nevertheless, Fisk refuses to give up his addiction to chasing foul balls.

Fisk hacks fans, too. Last week he clawed an Oriole foul away from a dozen grasping hands in Fenway Park. "Out," said the ump. Weaver stormed to the plate.

"The guy handed it to you, didn't he?" Weaver demanded as though he could get Fisk to confess to the umpire.

"Oh, no, Earl. I caught it," replied Fisk.

"Horse feathers," said Weaver, several times.

Fisk, Weaver and umpire then stood at home plate and watched the centerfield scoreboard replay show Fisk making the catch.

Weaver shook his head and for the first time in his decade of home-plate tirades broke into a smile.

"I gotta hand it to you, Fisk," he said.

So do a lot of other people.