פירוש על בבא מציעא 42:15

As it teaches, olives or carobs are prohibited - And you would think it is because they are not prone to fall and it cannot be said that [the finder] knew that [the owner] abandoned [them]. So even though once he will know, he will abandon [them], it is not [considered] abandonment from now.

Its appearance proves about it - It is known whose it is from its appearance. Hence once its owner knows that it fell, he will not abandon [it]. For he will surely say, "Everyone knows that they are mine and they are not ownerless, so they will not take them."