Humans routinely transmit and interpret subtle information about their mental states through the language they use, even when only the language text is available. This suggests humans can utilize the linguistic signature of a mental state (its mindprint), comprised of features in the text. Once the relevant features are identified, mindprints can be used to automatically identify mental states communicated via language. This paper focuses on the mindprints of eight mental states resulting from intentions, attitudes, and emotions, and present a mindprint-based machine learning technique to automatically identify these mental states in realistic language data. By using linguistic features that leverage available semantic, syntactic, and valence information, this approach achieves near-human performance on average and even exceeds human performance on occasion. Given this, it is argued that mindprints could be very valuable for intelligent systems interacting linguistically with humans.