The paper presents the results of transmission spectroscopy observations of the habitable zone exoplanet LHS 1140 b using the James Webb Space Telescope (JWST) NIRISS instrument. The observations, conducted during two transits of LHS 1140 b, capture a serendipitous transit of its inner companion, LHS 1140 c. The combined transmission spectrum of LHS 1140 b shows significant spectral contamination from unocculted stellar faculae, covering about 20% of the visible stellar surface. Despite this contamination, the analysis reveals tentative evidence of residual spectral features best-fit by Rayleigh scattering from an N₂-dominated atmosphere, with a significance of 2.3σ. Global Climate Models (GCMs) are used to rule out H₂-rich atmospheres of various compositions, confirming that such atmospheres are incompatible with the observed data. The GCM predictions also suggest that water clouds form below the transit photosphere, limiting their impact on transmission data. The observations suggest that LHS 1140 b is either airless or has a high mean molecular weight atmosphere. The tentative evidence of an N₂-rich atmosphere provides strong motivation for future transmission spectroscopy observations of LHS 1140 b to confirm this intriguing result. The paper discusses the implications of these findings for the habitability and atmospheric characterization of nearby exoplanets and outlines the necessary follow-up observations to further investigate the presence of a secondary atmosphere.The paper presents the results of transmission spectroscopy observations of the habitable zone exoplanet LHS 1140 b using the James Webb Space Telescope (JWST) NIRISS instrument. The observations, conducted during two transits of LHS 1140 b, capture a serendipitous transit of its inner companion, LHS 1140 c. The combined transmission spectrum of LHS 1140 b shows significant spectral contamination from unocculted stellar faculae, covering about 20% of the visible stellar surface. Despite this contamination, the analysis reveals tentative evidence of residual spectral features best-fit by Rayleigh scattering from an N₂-dominated atmosphere, with a significance of 2.3σ. Global Climate Models (GCMs) are used to rule out H₂-rich atmospheres of various compositions, confirming that such atmospheres are incompatible with the observed data. The GCM predictions also suggest that water clouds form below the transit photosphere, limiting their impact on transmission data. The observations suggest that LHS 1140 b is either airless or has a high mean molecular weight atmosphere. The tentative evidence of an N₂-rich atmosphere provides strong motivation for future transmission spectroscopy observations of LHS 1140 b to confirm this intriguing result. The paper discusses the implications of these findings for the habitability and atmospheric characterization of nearby exoplanets and outlines the necessary follow-up observations to further investigate the presence of a secondary atmosphere.