A total of 1,018 signs in one deaf child's naturalistic interaction with her deaf mother, between the ages of 19 and 24 months were analyzed. This study summarizes regular modification processes in the phonology of the child sign's handshape, location, movement, and prosody. First, changes to signs were explained by the notion of phonological markedness. Second, the child managed her production of first signs through two universal processes: structural change and substitution. Constraints unique to the visual modality also caused sign language-specific acquisition patterns, namely, more errors for handshape articulation in locations in peripheral vision, a high frequency of whole sign repetitions and feature group rather than one-to-one phoneme substitutions as in spoken language development.