Sign languages are perceived visually and externalized using the signer’s hands, face, and body. During sign language comprehension, deaf signers primarily focus their gaze on the face, while hearing non-signers attend more to the hands of a signer. It is not known whether deaf signers adapt their gaze behaviour when comprehending unknown signs. Here, we report eye-tracking data from 15 deaf native signers of German Sign Language (DGS) and 15 hearing non-signers who were presented with videos in either DGS or an unknown sign language, all containing no linguistic mouth actions. Our data confirm that deaf signers generally fixate more on the face of a signer than hearing non-signers who attend to the hands moving in sign space. Moreover, only deaf signers adapt their gaze behaviour and attend more to the hands when comprehending video stimuli consisting of unknown signs, suggesting similar adjustment behaviours as observed in spoken languages.