lawn sign liberal
A person who professes support for progressive causes (including Black Lives Matter, environmentalism, reproductive rights, LGBTQ+ rights, etc.) or political candidates by placing a lawn sign in their front yard while taking no other action to support these causes/candidates which will meaningfully contribute to advance of their goals.
Person 1: "Is Bill planning to canvass for Jimmy Carter?"
Person 2: "Nope."
Person 1: "What about sending postcards for Planned Parenthood?"
Person 2: "Nope."
Person 1: "So, how is Bill planning to help?"
Person 2: "Well, he put a sign in his yard. I guess he's just a lawn sign liberal."