In a down economy, displaying advertisements on an apartment building’s exterior might sound like a good way for a co-op board to rake in a little extra dough. But, as one co-op board learned at 59 Fourth Avenue, which was charged nearly $1 million by the city for illegal advertising displays, it’s relatively easy to get tripped up in the fine print. It’s important for property owners and boards to look through the laws and regulations that apply to their neighborhoods before jumping into an advertising arrangement, Carly Sullivan, a Department of Buildings spokesperson said. “The property owner may not even realize they need to get a permit — and they’re not necessarily told by the outdoor advertising company,” Sullivan said. Once you learn whether or not your neighborhood is properly zoned for outdoor advertising, it’s important to make sure that you’re working with a city-approved outdoor advertising company — getting on board with one that isn’t city registered could lead to conflict, according to Mitch Schwartz, vice president of Clear Channel Outdoor, an outdoor advertising company. “You’ve got to interview them, understand the legal parameters and stress that safety issues are paramount,” Schwartz said.