Walk by a Seattle restaurant today and you might notice a smiley face on the window. The emojis, which started appearing in January, indicate the business' food safety rating.

The scoring system may be the first of its kind in the United States. It rates restaurants on a four-point scale from “needs to improve” to “excellent,” with each category illustrated by an emoji. The higher their health inspection score, the happier the face.

The idea for the emojis builds on a growing movement to post health inspection grades on restaurants. Other large municipalities, such as Los Angeles County and New York City, require signs with letter grades that are visible to customers. The United Kingdom has a similar system for the entire country. The emoji system exists in China, but King County officials believe they're the first in America to use it.

“Society is demanding transparency. [Patrons] are demanding information in real-time as they’re making dining decisions,” says David Dyjack, executive director and CEO of the National Environmental Health Association.

In cases where the government doesn't publish health inspection scores, he says citizens do it on their own through social media and self-reporting websites.

The goal with the emojis, says Becky Elias, a section manager who oversaw the food ratings in King County, is not only to convey whether the food is safe to eat but to do it in a way that doesn't disadvantage non-English speakers.

King County's ratings system stands out for more than just its presentation.

In other cities, restaurants that receive a poor grade usually seek a do-over inspection, according to research by Daniel Ho, an expert in food safety grades from Stanford Law School who helped King County implement its program. Over time, he says grades get inflated and inspectors divert more of their time to handling appeals rather than conducting new inspections. To prevent that from happening, King County doesn’t allow do-over inspections.

That's sure to anger some business owners, but the most controversial aspect of the new system may actually be how the ratings are calculated.

Ho has found that ratings often vary by inspector, so a tougher inspector might mark down businesses in ways another might not. To account for differences in inspectors, the county rates a restaurant’s performance on a curve, relative to other restaurants under the same inspector's purview. It also takes into account the type of business, so a sushi restaurant won't be held to the same standards as a coffee shop.

The rating scheme King County settled on is also based solely on serious violations. According to Elias, other cities' systems don't adequately portray risk because their inspection scores reflect both serious health violations, such as workers not washing their hands, as well as smaller violations, such as inadequate lighting.

Sarah Schacht, who used Change.org to petition the county to post ratings after she caught E. coli food poisoning from a restaurant that -- unknown to her -- received “unsatisfactory” on five of its previous six health inspections, is a vocal critic of the system she fought for. She argues, for example, that the curving methodology the county chose to use misleads customers and obscures the true performance of a food business.

The county included restaurants early on and made adjustments based on feedback from them, as Elias points out.

Food safety grades can be controversial anywhere. In Colorado, businesses successfully lobbied the General Assembly last year to ban localities from instituting a “letter, number or symbol grading system, or a similar, oversimplified method of quantifying results.” Last week at a conference, the National Restaurant Association argued against restaurant grades in a debate with the director of environmental health for Los Angeles County. The association says grades aren't predictive of foodborne disease outbreaks and provide misleading, oversimplified summaries of actual risk.

In King County, however, the Seattle Restaurant Association backed the ratings system. Jillian Henze, a spokeswoman for the group, says the county included restaurants in discussions early on and made adjustments based on feedback from them.

"It was a picture-perfect partnership," Henze says.

For example, restaurant owners wanted the ratings to be based on long-term performance, not just the last inspection. That's why they're based on the most recent four inspections. Also, they wanted a four-point scale instead of three.

About half of all food businesses in King County fall into the “excellent” category, according to the public health department. Another 40 percent are in the “good” category. About 10 percent are “okay.” Roughly 1 percent are in “needs to improve,” which either means the restaurant had to be closed down temporarily or had so many serious violations that it requires follow-up inspections.

So far, Henze hasn't received complaints from members of the restaurant association, though only a quarter of the county's roughly 12,000 food businesses have received the emoji placards so far.

County health officials expected "there would be some heartburn from businesses," Elias says, but "overall it's been really smooth and really calm." Still, at least one restaurant posted a response beside the emoji defending their food safety. The county has also found some businesses posting placards in ways where the emoji is covered up by menus or other signs.

Schacht, the citizen who originally put pressure on the county to create a public ratings system, isn't satisfied with the final product and argues that county officials bent over backwards to appease business owners.

"Emojis aren't quantifiable, so they're more difficult to be shared as data," she says. "They essentially created a scoring system that is easier to be interpreted in person and challenging to be used online."

She also takes issue with the language of the ratings and the color scheme of the emojis, which are mostly gradients of green, a color she says assures customers that it's safe to eat at the restaurant.

"I don't think that many patrons in Seattle understand," she says, "that an 'okay' score is amongst the bottom 10 percent of open restaurants in your neighborhood."