Taking this guide as an example: https://www.fws.gov/sites/default/files/documents/Wildlife_Drive_Brochure_2019.pdf
My first thought is:
tourism=information
information=board
board_type=sight
operator=Blackwater National Wildlife Refuge
ref=1
name=Moist Soil Vegetation
I was initially thinking board_type=nature, but that seems to imply the that the board itself is inscribed with the interpretive info, rather than merely providing the reference to it. Other possibilities might by information=guidepost or information=route_marker, but those seem to be more for giving directions. tourism=viewpoint doesn’t feel exactly right either. Any other ideas?