OCEAN CITY, Md. — The print ad, which takes up most of a newspaper page, shouts, "The Ocean Is Evaporating!" TV and Internet spots warn that the world's oceans will disappear — in about a billion years. But what appear to be public service announcements this week, delivered with a fake sternness by Mayor Richard W. Meehan, are actually an ad campaign to encourage visits to the resort town. "We're advising citizens to book their Ocean City getaway now, before the ocean evaporates," Meehan says in the commercials; the image blurs and jumps like an old newsreel.