The pilot stated that he had just completed two touch-and-go landings in crosswind conditions without incident. During the takeoff roll following the third touch-and-go landing, the pilot retracted the flaps, turned off the carburetor heat, and gradually increased the engine power. He was applying control pressure to the ailerons and rudder to counteract the crosswind, and after the airplane reached a speed of 50 knots, the wind velocity reduced. The airplane then departed the runway to the left and collided with a runway sign, causing substantial damage to the fuselage.