In an effort to demystify the health score numbers posted at San Francisco food businesses, the city’s Department of Public Health will soon begin using red, yellow and green placards that restaurants must post in their windows.

The department announced the new visual aspect of the scoring system on Wednesday to coincide with the start of San Francisco Restaurant Week, which began Jan. 22 and runs through Jan. 31. The system was approved on Nov. 5 by the city’s Board of Supervisors. The placards, which will also go on food trucks, will be implemented in early spring.

The San Francisco Department of Public Health currently issues health inspection scores on a 100-point scale. Though full inspection reports are available to the public on the department’s website, most diners walking into an establishment don’t know what differentiates a score of 80 or 90. The new placards, which are similar to those already used in other Bay Area cities and counties, will use three colors to quickly convey inspection results.

A green sign will mean a restaurant is “good to go,” and has passed its food safety inspection, according to a statement from the department.

Yellow will indicate diners should use “caution” because the business has two or more issues that must be corrected before its re-inspection by the department.

“Red means stop,” according to the department. A red card will appear when a business is forced to temporarily close until its health issues are corrected.

“San Francisco has approximately 7,000 food facilities,” said San Francisco Department of Public Health spokeswoman Veronica Vien. “They will all be subject to the new system.”

The department statement said the placards “will reflect real-time operations after a food safety inspection.”

“Not only can we better inform the public, we are also supporting small businesses by simplifying a system that promotes public safety, trust and transparency,” Supervisor Aaron Peskin said in a statement.

Elected officials have attempted to simplify the city’s numeric system since at least 2004, when then-Supervisor Chris Daly advocated a letter-grade system for restaurant inspections, which Los Angeles and New York began using at the time. Instead, San Francisco stuck to its numeric system.

Color-coded health inspection placards are now common in numerous cities on the West Coast including Seattle, Anaheim, Irvine and Huntington Beach.

Justin Phillips is a San Francisco Chronicle staff writer. Email: jphillips@sfchronicle.com Twitter: @JustMrPhillips