Protest placards are an important part of School Strike 4 Climate (SS4C) protest culture and illustrate how protesters view, understand and share their environmental concerns. Many of the placards use humor to convey the messages of their creators. Bringing together science communication and humor studies, this paper examines the communicative functions of humor in Australian SS4C posters by asking to what extent protest signs can be understood as a vehicle of science communication. The paper reveals how humorous protest placards become the means of grassroots creativity, exploring bottom-up science communication in an ambiguous, but accessible and enjoyable form.