Administrative innovations in South-west Asia during the fourth millennium BC, including the cylinder seals that were rolled on the earliest clay tablets, laid the foundations for proto-cuneiform script, one of the first writing systems. Seals were rich in iconography, but little research has focused on the potential influence of specific motifs on the development of the sign-based proto-cuneiform script. Here, the authors identify symbolic precursors to fundamental proto-cuneiform signs among late pre-literate seal motifs that describe the transportation of vessels and textiles, highlighting the synergy of early systems of clay-based communication.