Here's your sign for the March For Science, or the People's Climate March! Crowdsourced from March For Science members, from a concept by Brian Nguyen,
Download it, print it on 11 x 17" paper, glue it onto some cardboard, tape on a stick, and you have got a sign! A paint stirrer or a paper towel tube make excellent handles.
You can find other signs, including my "Scientists March for Science" designs customized for: Archaeologists, Artists, Astronomers, Biologists, Chemists, Climatologists, Educators, Engineers, Geologists, Librarians, Mathematicians, Medical Professionals, Nurses, Oceanographers, Physicists, Programmers, Science Teachers, and Writers, here: