Signs up is a term that refers to the act of enrolling or registering for something. Antonyms for signs up could include dropping out, opting out, withdrawing, or canceling. These terms are used to indicate the opposite of signing up for something. Dropping out refers to quitting or ending participation in a program or course. Opting out means to choose not to participate in something, and withdrawing involves removing oneself from a situation or agreement. Canceling is the act of nullifying or revoking something that was previously agreed upon. All of these antonyms convey a sense of disengagement or non-participation in contrast to the action of signing up.