For me it was 3 games that finally made me think that it wasnt a tease and they were really back. The game against the Falcons in late 1994 when Favre ran the ball in for a TD and the Christmas Eve game against the Steelers in 1995.
But the one game I truly and finally believed the Packers were truly back was the divisional playoff game at home against the 49ers in the snow, rain, ice, and mud. I KNEW after they won that game they were truly back and were going to actually win it all.