When he first spotted the strange graffiti, Mushtaq Hussain thought it was a juvenile prank: Somebody had used bacon strips on a sidewalk in front of a Florence, S.C., mosque to spell out the words "PIG" and "CHUMP."

But as Mr. Hussain, a board member at the Islamic Center in Florence, gave it some thought, the incident last Sunday seemed less like an ill-advised gag and more like a cunning and cruel affront. "We thought seriously, and we thought, ‘You know, somebody doesn't like us,' " he told WMBF-TV news in Florence.

Nationwide, polls show a growing ambivalence – or even anger – toward Islam among Americans, which has in part explained the opposition to a mosque near ground zero and mosques elsewhere, as well as the aborted mass burning of Korans by a Florida preacher. But subtler, more psychological attacks against Muslims have also become prevalent, say Muslim groups.

WATCH VIDEO: Build a 'mosque' near ground zero?

In those attacks, pork – which Muslims are forbidden to eat because it is considered unclean – is being used as a primary weapon, sent in packages to mosques, invoked in sharply worded letters, or, as in Florence, used to spell out literal messages.

To many experts, pork-laden messages, such as the one delivered in the heart of the barbecue belt last weekend, mirror what appears to be an increasingly conflicted view in America about the impact of Muslim culture on US politics and society.

Like protests such as "Everybody Draw Mohammad Day," some Americans are needling what they perceive to be an over-sensitive Muslim population with acts that – to non-Muslims – seem relatively tame. In the process, they are exposing the vast difference between what is considered acceptable by the measures of American free speech and by the believers of Islam.

"These are not hate crimes, but they're expressions of intolerance, really," says David Schanzer, director of the Triangle Center on Terrorism and Homeland Security at Duke and the University of North Carolina, Chapel Hill. "I think a lot of this is generated by a lack of understanding, anger about 9/11, and a great deal of misinformation about Muslims in America and Islam, all of which is in plentiful abundance on the Internet and on blogs."

Pork as a weapon

According to the Council of American-Islamic Relations (CAIR), attacks on mosques, cases of Americans burning and even shotgun-blasting Qurans, and personal confrontations on streets have ticked up in recent months. Such claims are hard to quantify, experts say, because more people may simply be reporting incidents that went unheeded in the past.

Anecdotal evidence points to the use of pork as an anti-Islamic protest in recent years. For example:

In September, the US Postal Inspection Service reported that at least four packages containing hate letters and bacon were sent to American mosques from Denver. CAIR is a regular recipient of pork-related hate mail.

In March, two Minnesota high school students allegedly shoved bacon in the faces of several Muslim classmates, according to a CAIR complaint.

In 2007, a Texas farmer held afternoon pig races on Friday – the Muslim holy day – to protest a proposed mosque next to his farm.

In 2006, a severed pig's head was thrown into a Maine mosque during prayers.

Overseas, 7,000 protesters held a "pork sausage and booze" party in Paris this summer, which was designed as a provocation against Muslims and a protest against the perceived Islamicization of France.

On the Internet, bloggers are invoking pork to incite Muslims. In a recent column on the conservative Town Hall.com, Mike Adams, a criminology professor at the University of North Carolina, proposed several pork-related pranks against the "ground zero mosque," including "building a large bomb filled with bacon grease. Dubbed the 'Mother of All Bacon,' or MOAB, this bomb would not hurt anyone but would permanently defile the location so that no one could worship there."

"The problem is you could look at [such incidents] and say, 'Oh, well, it's just some idiot doing something stupid,' but I think it should be viewed against the overall rise of anti-Muslim sentiment in society," says Ibrahim Hooper, director of CAIR. "Right now, the whole pork theme is quite popular with the Muslim haters out there."

Weariness with Muslim sensitivities

The pork attacks come amid tensions in the US about how to talk about Islam in popular culture. A Seattle artist who proposed – then withdrew – a call for a "Everybody Draw Mohammad Day" in protest of a censored "South Park" episode, recently left her job, moved, and changed her name on the FBI's advice after radical cleric Anwar al-Awlaki issued a fatwa for her death, the New York Post reported last month. Islam forbids the depicting of the Prophet Mohammed.

In light of such stories, as many as 1 in 5 Americans are incensed that they have to tip-toe around Muslim sensibilities in a country where the First Amendment guarantees nearly all speech, including hateful words and acts.

So is pork a crime?

The bacon graffiti this weekend prompted CAIR to call on the FBI to investigate what they called a "desecration" that took place as part what the organization says is a broader pattern of intimidation being waged against Muslims around the US.

So far, police in Florence say the incident doesn't meet the criteria for a hate crime, but they are investigating the incident as a case of harassment.

Critics of Islamic culture in the US see CAIR's concern about the bacon attack as part of "stealth jihad" in which US-based Islamic groups demand that Muslim sensibilities be protected at all costs, all in a larger effort to make the US "Sharia compliant," abiding by the edicts of Islam.

"If Christians are expected to endure crucifixes submersed in jars of urine being represented as art, then Muslim Americans had better develop an appreciation for the attributes of the society in which they live and don thicker skins," writes a blogger on PipeLineNews, which posits itself as a group of investigative journalists focusing on the culture wars and national security.

American views of Islam slip

The share of Americans who have a "favorable view" of Islam has dropped from 41 percent five years ago to 30 percent today, according to an Aug. 24 Pew Forum on Religious and Public Life survey. Concern about Islam's influence on US society has entered the national political arena, as well, shown by a different Pew poll that found that 1 in 5 Americans believe President Obama is a Muslim – an 11 percent jump since a year ago.

"A lot of it has to do with the economy. There is a sense that life is unstable. The American public is under siege," John Green, director of the Bliss Institute of Applied Politics at the University of Akron, told the San Francisco Chronicle this summer. "So, foreign threats are magnified. In a lot of people's minds, there is this sense that this religion is associated with violence."

Experts like Mr. Schanzer fear that protests like the bacon graffiti in Florence can backfire.

"Besides it being inconsistent with American values, I think it's damaging to our security," he says. "There's no doubt that one of the best ways to prevent homegrown terrorism is to get good information from the Muslim community, and that is made much more difficult when Muslims feel there's a climate of intolerance in the country."

WATCH VIDEO: Build a 'mosque' near ground zero?