A compelling body of research suggests that students from racially marginalized and minoritized (RMM) backgrounds are systematically deterred from Science, Technology, Engineering, and Math (STEM) fields when teachers and scientists create ideologically colorblind STEM learning environments where cultural differences are deemed irrelevant and disregard how race/ethnicity shapes students' experiences. We examine whether and how STEM faculty can serve as important sources of information that signal racial/ethnic diversity inclusion (or exclusion) that influence RMM students' motivation to persist in STEM. Specifically, we focus on RMM students' perceptions of their faculty research mentors' cultural awareness--the extent to which students believe that their faculty research mentor acknowledges and appreciates racial/ethnic differences in STEM research. Results from a longitudinal survey of RMM students (N = 150) participating in 74 faculty-led STEM research labs demonstrated that RMM students who perceived their faculty research mentor to be more culturally aware experienced more positive "social climates" in the lab and were more "identified as scientists." Increased science identity, in turn, predicted their motivation to pursue STEM careers 3 months later. These findings demonstrate the importance of acknowledging, welcoming, and celebrating racial/ethnic diversity within STEM learning environments to broaden inclusive and equitable participation in STEM.