And you would be right! Burning ballots results in black smoke. In order to turn it white, the cardinals are given a packet to be tossed in with the final ballots that is supposed to generate white smoke. It didn't work quite as planned when Joseph Cardinal Ratzinger was elected.
The smoke looked more grey than white. The tip off, however, is the tolling of the bells on St. Peter's. Someone mentioned the other day that each bell has a name. The largest one is St. Andrew's bell, named for Peter's brother.
The largest of the bells - campanone has a diameter of 2.50 meter, a height of 2.60 meter, measuring 7.5 meters in circumference and weighing about 11 tons. It was cast in 1786 by Luigi Valadier and blessed by Pius VI in the same year. Since 1931, the bells are operated electrically, thus permitting even the largest bell to be tolled from a distance. It is rung at Christmas and Easter, on the Solemnity of Sts. Peter and Paul, and every time the Pope imparts the "Urbi et Orbi" blessing (to the city and to the world). It is also rung on the election of a new pontiff. The note of this bell is E3.