It’s not unusual during a political season for campaigns to tear down rivals’ campaign posters. The practice almost comes with the territory of seeking public office. Aside from public debates, poster hanging has long been the most inexpensive way for a candidate to get exposure. In a crowded race, a candidate would like to see as few as possible of his rivals’ posters.

The other night, while pulling out of the parking lot at work, I spotted on a pole a freshly hung poster of a candidate running for Manhattan borough president grinning down at me. The poster urged me to cast a vote for him and to visit his Web site. The next morning, that poster was gone, replaced by a different grinning candidate vying for the same office, who also urged me to vote for him and to visit his Web site. It doesn’t take an ace detective to figure out that during the wee hours of the morning, some low-paid staff member or campaign volunteer – or, who knows, maybe the second candidate himself – made the swap.

Sadly, in some ways, I almost expect that behavior from campaign aides, bent on getting their candidate elected. But I’m disturbed when city agencies and departments, which are supposed to remain nonpartisan, engage in similar acts of malfeasance.

That’s what happened when the New York Police Department decided several weeks ago to tear down C. Virginia Fields’s posters from barricades set up during the Carnival del Boulevard parade. Oddly, Mayor Bloomberg’s signs were left in place. The other Democratic candidates vying to take on Mr. Bloomberg in the fall have reported that somehow their posters, too, always mysteriously disappear from police barricades at various citywide parades.

A police spokesman, Jason Post, says it’s illegal to hang campaign posters on police barricades, adding that police officers are within their rights to yank them down.

“Nobody can hang anything on a police barricade,” he said, dismissing charges by the Fields camp that Mr. Bloomberg has received preferential treatment. Though Mr. Post said Mr. Bloomberg’s posters have repeatedly been taken down, at last Sunday’s Dominican Day parade, the barricades that lined the street prominently featured dozens of them. And while police officers may have been too busy tending to other matters to take them down, they remained up for hours for thousands of spectators to see.

“We are treated like everyone else’s campaign,” Stuart Loeser, a spokesman for Mr. Bloomberg, said. He said Mr. Bloomberg’s camp is aware that the signs should not be placed on the barricades but said staff members and volunteers remove them after the event is over.

Ms. Fields’s campaign manager, Chung Seto, recently wrote a letter of complaint to the police commissioner, Raymond Kelly.

“If the department decides to enforce posting regulations, it should not engage in a selective and discriminatory manner,” Ms. Seto wrote. “To allow the Mayor’s campaign material to be displayed while intentionally removing an opponent’s posters raises troubling questions about the impartiality of the New York Police Department. It is highly improper and intolerable for police officers to engage in selective enforcement.”

Once she was informed that it was unlawful to hang signs from the barricades, Ms. Seto said, she ordered her staff and volunteers to cease doing so, and she had no posters hanging from the barricades at last Sunday’s parade.

Asked why Mr. Bloomberg’s campaign continues to hang posters from the barricades, even though it has been warned that the practice is illegal, Mr. Loeser said, “We do it because other campaigns do it.”

At issue here is not the hanging of posters from police barricades, but consistency and fairness. Mr. Bloomberg should get involved personally and pledge that his camp will adhere to the same guidelines the Democrats have been asked to follow. Here’s a simple solution: that no campaign hang posters from police barricades.

Though Mr. Bloomberg is leading in the polls and has gained growing support in the city’s black community, a base that historically does not vote Republican, he must be careful not to assume that the race is all but a done deal. His reluctance to participate in mayoral debates, for example, could provide problems for his campaign, as residents want to hear from the mayor about the problems that continue to beset the city: failing schools, a lack of affordable housing, and high unemployment rates among black men.

Though hanging posters on police barricades may seem insignificant, Mr. Bloomberg can’t afford not to address the issue. At the end of the day, voters want to know that their political leaders are playing by the same set of rules.

Mr. Watson is the executive editor of The New York Amsterdam News. He can be reached at jamalwats@aol.com.