WESTMINSTER -- From a distance, the plane rolling up and down with its 252 lights flashing on and off could have been mistaken for a UFO.
But from a seat in Oriole Park at Camden Yards, its purpose was clear.
Advertisements for real estate agents, radio and TV stations, restaurants and taverns flashed brightly to the crowd below from the "sky sign" -- a grid of lights attached to the wings of a Cessna 172.
The sign, owned by a two-month-old Carroll County company, made its debut at an Orioles game Aug. 3.
"It's unique and different, and people are going to remember it," said June M. Poage, part-owner of Eastern Aerial Advertising Inc.
An ad for the Mount Washington Tavern in Baltimore was among those flashed to the crowd of baseball fans last week.
General Manager Rob Frisch said Eastern Aerial tried the new mode of advertising because it was "a fairly inexpensive way to hit a large group of people."
The average price for an ad, which runs at least 20 times during a ballgame or other event, is $200 to $300, Ms. Poage said. The company charges by the letter or character.
The price for a customer who wants to buy a one-time "Happy Birthday" or personal ad would be less, she noted.
Pilot Brad J. Kline, 32, of Finksburg, flies the small plane. His wife, Laura, 34, usually sits beside him and operates the portable computer that controls the lights.
The Klines also are part-owners of Eastern Aerial Advertising.
Westair Inc., which leases Carroll County Regional Airport from the county, rents the plane to the advertising company. Ms. Poage is the president of Westair.
Mr. Kline, a pilot for eight years, also is a Westair employee. He is a flight instructor at the Carroll airport and flies for Metro Traffic, a Washington service that reports on traffic conditions and contracts with Westair for pilots and planes.
Mrs. Kline works three days a week as a hairdresser and plans to learn to fly planes.
Eastern Aerial Advertising bought the sky sign from Tom Foster, a Miami man who designed and patented it.
Mr. Foster has sold about 30 of the signs in the United States and others in Europe, Mr. Kline said.
The sign works in the same way as the lighted sign on the Goodyear blimp, Mr. Kline said.
The aluminum grid, which weighs about 100 pounds, is 36 feet long -- the same as the plane's wingspan -- and 8 feet wide. It's attached to the plane's wings.
The tiny 24-volt lights, about the same size as flashbulbs or Christmas tree lights, are attached to the grid under small silver reflectors.
Advertisements are typed into the portable computer, which is connected to a black box in the back of the plane that contains the electrical source for the lights.
The computer can handle 54,000 characters. It can do company logos, but it can't do intricate graphics, Mr. Kline said. It can flash the ad message, roll it or move it from right to left. It also reverses the message if a crowd is behind the plane.
The message is visible to a crowd from a 30-degree angle in front of and behind the plane, he said.
Ms. Poage and the Klines said they plan to fly over the Inner Harbor, Merriweather Post Pavilion, the Maryland State Fair and RFK Stadium.