A’s fans may want to know one thing before they set off for a game at O.co Coliseum this spring: No signs larger than 3 feet by 6 feet will be permitted.

The team has never had a policy for the size of banners brought into the stadium.

But the front office said homemade signs fans brought into the stadium were having a “negative aesthetic impact.”

Team officials decided during the offseason to implement the 3-by-6 policy after researching restrictions at other stadiums, spokesman Bob Rose said.

Some believe the decision is intended to make messages critical of co-owner Lew Wolff harder to see.

The policy follows a 2010 episode involving a fan being ejected from the game for sheet-sized banners criticizing Wolff for his efforts to move the team to San Jose. Two of them read, “Lew Wolff lied, he never tried” and “Don’t take our A’s away.” Such negative messages are rare in the stadium. Most signs are aimed at ballplayers, not owners.

The fan, Jorge Leon, is a Baseball Oakland booster dedicated to keeping the A’s in Oakland. The banners were meant to be visible to other fans and the media. The strategy worked.

But kicking Leon out backfired. The team couldn’t prevent him from attending games after then-Oakland City Attorney John Russo called the ouster an unconstitutional infringement on the free speech rights of fans.

That didn’t stop the A’s from cracking down on banners again during Fanfest on Jan. 29. Leon and other fans who showed up with the same banners critical of Wolff were told by guards they couldn’t display the banners in Oracle Arena.

The team hosted Fanfest in the arena, which sits adjacent to the stadium in the Coliseum complex. Leon said the guard told him to put away the banners and said they couldn’t yell, “Lew Wolff sucks,” because “it’s a family environment.”

The A’s said the team determined prohibiting banners and noisemakers was in the best interest of Fanfest attendees. The team said no one is restricted from expressing an opinion as long as it’s done in good taste and doesn’t single out a player in a harmful way.

Those are the criteria Russo said were not sufficient to limit speech. Lawsuits against banner restrictions at RFK Stadium in Washington, D.C., and Great American Ball Park in Cincinnati came to the same conclusion: Any restrictions on speech may not be based on the subject matter of the sign unless justified by a compelling state interest. That would include signs that incite violence, contain obscenities or other criteria.

“In other words,” Russo wrote at the time, “the A’s may not prohibit fans from speaking their minds about his ownership of the team,” meaning Wolff.

As for the 3-by-6 sign limit, the team said the policy does not restrict opinion and is within industry standards, citing the Los Angeles Dodgers, who do not allow any banners. The Seattle Mariners, Los Angeles Angels and other baseball teams tend to place a 3-foot height limit on signs, according to the A’s.

Oakland City Attorney Barbara Parker did not provide a comment about the new sign policy. Alameda County Counsel Donna Ziegler said she could not comment on a policy with which she is not familiar. The Coliseum’s governing body, the Joint Powers Authority, has no policy on signs, Executive Director Marc Kaufman said. Alameda County and the city of Oakland share ownership and oversight of the Coliseum complex.

That appears to leave the decision about size up to the A’s during team events.

Leon said the policy won’t deter him and fellow boosters.

“We will find a way to speak our mind,” he said. “We’ll figure out a way to keep up the fight.”