At the local church of Jesus of Latter Day Saints (which actually resembles a public swimming bath circa 1970), there is a large granite sign fixed to the wall to inform you that visitors are welcome.
Well I should like to add the proviso “not if those visitors are pigeons they are not.”

But Sparky squirrel here has realised that what was designed to keep pigeons off/away/out has actually provided it and its family with a vast fortress to live in safely out of the reach of cats.