Nearly a year ago, Gov. Jerry Brown of California signed a law requiring the state’s colleges and universities to adopt an "affirmative consent" standard defining that "only yes means yes" — that students engaging in sexual activity must signal they are willingly doing so. Now other states are making — or at least weighing — similar moves. Gov. Andrew M. Cuomo of New York signed a law this month requiring affirmative consent on college campuses, and advocates of the practice say it is likely to spread elsewhere. The momentum is a sign that lawmakers and colleges continue to sharpen their focus on thwarting campus sexual assault while encouraging students to report attacks.