Requires strong teeth.
It's not actually incorrect, but I would have been happier had the signmaker put an "s" on the "edible" to clarify that the word is being used as a noun, not as an adjective.
(I wanted to put "something else" into the pit toilet)
Both signs photographed at the University of Minnesota's Landscape Arboretum this past week.
On the subject of ambiguity I'll also mention that several discussions of the current scandals involving the National Football League have included comments by "Domestic Abuse Advocates," who presumably would not refer to themselves in that fashion...