Aesthetics was viewed by Croce as the heart of philosophy because it was that which the individual immediately confronts in the moment. It is only aesthetics which allows any real change for an individual. He viewed the distinction between natural and conventional signs as invalid. Painting is an example he gave of natural signs--that is--- everyone could understand them without knowing the verbal language of the painter. Conventional signs might be the words used in poetry, so it was not immediate and intuitive. Croce argued against this view, by basically pointing out that there were no really natural signs. The example he used, which I assume must have had some currency in the era in which he was writing, was a painting of a man. This portrait was supposed to be able to elicit happiness from the man's wee children, and even the dogs and cats in his household. The responses from such non-verbal beings was held as an example of the validity of natural signs. Croce insisted though, that such "natural signs do not really exist". He pointed out anecdotes about tribes that thought a painting of a man on horseback showed a man with only one leg, as evidence that should "undermine our faith in sucklings, dogs and cats who understand paintings. "
This example of Croce's philosophy he expounds originally in L'Estetica come scienza dell'espressione e linguistica generale (1902).