Here are three bits of wisdom garnered from a recent interview with Dan Matthews of Matthews Auctions, Nokomis, Illinois. His auction company specializes in antique advertising.

This Harbor Petroleum sign sold for $8,250. Condition kept the price to four figures. (Photo: Matthews Auctions)

* When it comes to advertising, condition is paramount. At a June 2013 auction, Matthews sold a Harbor Petroleum Products sign for $8,250. The sign was rated a modest 7 on one side and 6.5 on the other (on a 10-point scale). “Seven or eight [thousand dollars] is a lot for a sign in that shape,” Matthews said. Better examples have brought considerably more. “I sold one for $40,000, and I sold one for $55,000.”

* Signs continue to be one of the blue chips of the advertising market. “Signs progressively go up in value every year, whether it’s 2 percent or 10 percent or 20 percent,” Matthews said. “Signs have steadily gone up the last 10 or 15 years. Globes, oil cans and even gas pumps have gone up and down more erratic than signs have.” Supply and demand play a major role. For every buyer of a gasoline globe, there are 25 or 30 people interested in signs, which are easy to decorate with and typically aren’t fragile.

* Any size sign can bring serious interest, depending on the subject matter, condition and rarity. As a whole, however, smaller signs are the mainstay of the market. “Your best stuff is your small items, 30-inch signs or less, and pump plates,” said Matthews.