Signed languages exploit the visual/gestural modality to create iconic expression across a wide range of basic conceptual structures in which the phonetic resources of the language are built up into an analogue of a mental image (Taub, 2001). Previously, we demonstrated a processing advantage when iconic properties of signs were made salient in a corresponding picture during a picture and sign matching task (Thompson, Vinson, & Vigliocco, 2009). The current study investigates the extent of iconicity effects with a phonological decision task (does the sign involve straight or curved fingers?) in which the meaning of the sign is irrelevant. The results show that iconicity is a significant predictor of response latencies and accuracy, with more iconic signs leading to slower responses and more errors. We conclude that meaning is activated automatically for highly iconic properties of a sign, and this leads to interference in making form-based decisions. Thus, the current study extends previous work by demonstrating that iconicity effects permeate the entire language system, arising automatically even when access to meaning is not needed. (Contains 5 footnotes and 2 figures.)