This is the Cabin numbers and the greek gods symbols. With Percy Jackson's camp (Camp-halfblood) all the cabins have names and symbols.
Found this Camp half blood cabin layout map. Except it doesnt fit the book. The girls were the even numbers to the left from Hera's cabin. Iris is then on the wrong side and so is Nike
Daily Activity Schedule - Welcome to Camp Half-Blood: The Online World of Rick Riordan