Applied neuroscience presently allows not only the scientific discovery-oriented probing of the inner workings of the mind, but increasingly the probing of individual minds toward gathering intelligence. Significant advances in neuroimaging, leveraging both active and passive electro-optical energy, can reveal specifics of information held in the mind even without cooperation (e.g., Lange et al., 2018; Sawyer et al., 2016a). The processes of the brain increasingly join many other energetic sources from which quantitative and qualitative data analysis may extract identifying features and other useful intelligence (Sawyer & Canham, 2019). Indeed, it is increasingly appropriate to discuss the human brain as a system which can be read from, written to, and the operations of which may therefore be collected for analysis or influenced (Sawyer & Canham, 2019). We argue here that we are witnessing the end of the era in which human thought is generally accepted as an entirely private process, the starting point of an unquestionably remarkable transition. The collection of unintended emissions and byproducts toward intelligence fits well into the mold of Measurement and Signals Intelligence, and indeed Measurement and Signature Intelligence (both MASINT, Macartney, 2001), and so we believe this community within the Intelligence Community is wellsuited to discuss these new realities of neurosecurity, as it helped shape many formative discussions surrounding cybersecurity. A MASINT perspective on biological, neural signatures comes with the need to discuss current capabilities, projected technological arc, practicalities, and potential abuses.