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Two red, two yellow.

What sounds like a child sorting Halloween hard candies this year doubles as something a bit more important to state and federal disaster-management officials: the Waffle House Index for Hurricane Sandy.

Two Waffle Houses near Allentown, Pa., were closed, and two in Maryland were open but serving a limited menu, according to Waffle House spokesperson Kelly Thrasher. All were without electricity; the open ones had gas and water.

Thrasher summarized the Index: when an official phones a Waffle House and the restaurant is open and serving the full menu, the index is Green. When the restaurant is open but serving a limited menu, it's yellow. When it's closed, it's red.

Federal Emergency Management Administration head Craig Fugate devised the index after leading Florida's response to several hurricanes in the 2000s. Based on the 24-hour restaurant chain's hardy reputation and presence across the Southeast, it is an informal yet handy way to assess an area's post-calamity condition.

This allows officials to do quick disaster-relief triage: red areas need help first, and fast.

Thrasher said Hurricane Isaac closed 40 restaurants on the gulf coast for a few days. She attributed the difference between this and Sandy to the chain's high concentration of restaurants in the gulf area. Their restaurants in Virginia, Maryland and Pennsylvania are fewer and more spread out. There are no Waffle Houses in New Jersey or New York.

In addition, the company was "definitely proactive" before Sandy hit, Thrasher said. They tracked the storm all last week and sent an advance team pre-landfall with extra supplies and employees.

The Waffle House Index has its own hashtag. "How can the severity of Sandy be measured? The northern most WaffleHouse is in Ohio. #WaffleHouseIndex," a Twitter user [@rkeni2] tweeted yesterday.

Thrasher called the attention "very flattering," but added: "This is what we do all the time: to be there for our customers and associates on an everyday basis."

A call to FEMA went unreturned. Perhaps they were busy calling Waffle House.

Watch the full story on a special "20/20? tonight at 10 p.m. ET