Just a warning for those who think flying a banner across the sky or buying a billboard extolling the virtues of your favorite team in enemy territory is something good fans do. Some may think it’s “fun.” If so, call me the fun police.

I generally veer on the side of extreme leniency when it comes to in-game celebration, either by players or fans. They do it right in Latin America, whether the game in question is béisbol or fútbol. It’s only a game, so express yourself however you wish … at the game, either on the field or in the stands.

Buying a billboard or flying a banner over a stadium brings none of that spontaneity. It’s a premeditated symbol designed to annoy from a safe distance, the equivalent of sticking out one’s tongue and yelling “Neener-neener” from behind bulletproof glass.

The money involved is irrelevant. People waste their money on stuff like boutique bottled water, private jets, stupid cars, drugs and Barry Zito all the time. But this trend is real, and it must be stopped. And there’s no better way to halt a trend than some good old-fashioned mockery.

The Latest: the 49ers Championships Billboard

49ers Billboard How Many Do You Have

Pros: The written copy is an actual sentence; nice homage to “The Catch”; money raised beyond the cost of the billboard ($7,000) is going to charity.

Cons: Off-the-charts smugness; 49ers fans are officially obsessed with the past (San Francisco last won a Super Bowl back when Ace of Base was popular); “The Catch” didn’t happen during a Super Bowl.

Two weeks ago: the Seahawks Airplane Banner

Pros: Easily the most polite sign of the three included in this post; relatively unobtrusive; only flew around above Candlestick Park for about 20-30 minutes.

Cons: Difficult to read; the banner doesn’t have much to say (they must have had to pay by the character); Seahawks fans have a bad habit of rooting for themselves — just check out how many Seahawks fans wear No. 12 jerseys with “FAN” as the name on the back while referring to themselves as “12s.”

The one that started it all*: Opening Day 2011 at Dodger Stadium

*I’m sure someone will bring up another fan billboard or banner that was designed to tweak another group of fans, but this is the first one I remember. #research

Dodgers Still Suck Airplane Banner SF Giants

Pros: Nice long banner; lots of letters here; no misspellings.

Cons: Devoid of cleverness (another trend emerges!); “FROM SF CHAMPS FANS” reads like something Google Translator spit out; the guy who paid for this talked about it so much that Dodgers fans had time to put together a preemptive response.

LA 5 SF 1 Giants Suck

I guess the first part, which looks like “LAS,” is supposed to read “LA 5,” as in number of championships since the two teams moved out west. The lesson: when you buy a banner or a billboard designed to troll another team’s fans, no one ends up looking good. Leave the banners and billboards to corporate advertisers.