Finite-size aerosols under chaotic advection often approach a strange attractor. They move chaotically on this fractal set but, in the presence of gravity, they have a net vertical motion downwards and precipitate. In many practical situations, information of the advection dynamics of the aerosols is fundamental, whereas only precipitation data are available. We uncover two fractal signatures of chaotic advection in precipitation. Each one enables the computation of the fractal dimension D_0 of the strange attractor in the physical space without prior knowledge of the advection dynamics. We illustrate our theoretical findings with a numerical experiment and discuss their possible relevance to meteorology.