At about 14:23 mountain time, a Cessna 172M struck an airport sign during takeoff from Love Field. The flight instructor and his student flew in the vicinity of the airport and evaluated the damage to the airplanes right main landing gear. At 14:40, the CFI landed back at the airport and the right main landing gear collapsed during rollout. The CFI said they were working on crosswind takeoffs and landings and selected runway 21R when the winds were from 120 at 11 knots.