I manage a garden all maintained and plants paid for by volunteers in a federal, state, and city historic landmark managed in whole by the parks department. Most visitors have no idea of any of the above. What is very clear is that this is a cemetery. People still take whatever they want right off of a grave. Our parks in California are off limits for "taking" plant or any other material. If it isn't yours the answer seems very clear in all cases. Don't help yourself to what is not yours.
