This proverb means that even if a person is wicked, they will not have external attributes or characteristics to identify them as such. Horns are often associated with demonic or evil creatures, and this proverb suggests that wickedness does not have a recognizable appearance. In other words, one should not judge people by their appearance, as malevolent behaviors are not always visible. The equivalent French proverb could be: ‘L’habit ne fait pas le moine.’