Atlantic City, New Jersey — The air inside Atlantic City’s casinos was notably cleaner Sunday, as a restrictive new smoking law took effect. Well-placed signs let gamblers determine which areas were OK to smoke in, and only a few patrons had to be reminded not to light up in no-smoking areas. The new law restricts smoking to no more than 25 percent of a casino’s floor. It went into effect Sunday, exactly a year after New Jersey’s Smoke-Free Air Act prohibited cigar, cigarette and pipe smoking in restaurants, bars, private office buildings and other indoor places.