You would think that it would not be necessary to tell people this. But, to be fair, the problem that the museum faced is that people were climbing on the life-size models of the whales for, presumably, photo opportunities.
Rosemary Marco, a naturalist and the artist behind the nature-themed webcomic Bird and Moon, shares this photo. She says that it’s from a whale museum in Quebec. I’m going to guess that it’s the Marine Mammal Interpretation Centre in the town of Tadoussac. Online photos of it show a wide variety of model whale skeletons online. Only such a sign could keep tourists off them.