If we can trust our samples, on Madeira road workers imported from mainland Portugal wouldn't attract attention on Madeira. Imported rocks however could raise suspicion and maybe even trigger alert. The local rocks are a kind of their own and stand apart from their Portuguese counterparts.
Some panels even show a pile.
The cliff is reminiscent of the ocean. The rock signs on the Azores seem very much influenced by designs from the continent. Probably imported from Spain . Find the very same sign in Portugal .