We might always be partial to anything Neil deGrasse Tyson-related, so while brainard1121's sign that science is true whether or not you believe in it is a favorite, other signs for tomorrow's March for Science posted at Stat News might tickle others' fancy.
There's a Futurama-inspired one for fans of science, sci-fi, and Professor Farnsworth, as well as one calling on researchers to be like bacteria and resist. Quartz also highlights signs used at previous protests including one that says "Protests Change Things" with a citation to a study at the bottom as well as a sign asking for evidence-based science, but only after peer review. The march organizers themselves have some signs at their site that people can download.
There are also sign-making parties going on where you can get your poster board and Sharpies on, such as one at Genspace in Brooklyn.
But as we don't see a witty genomics one yet — something with gnomes, maybe? — do you have any ideas, dear readers?