= Solution
Three observable signatures are \b[a blue optical transmission slope, muted molecular transmission features, and enhanced reflected optical light].
Small-particle <atmospheric haze> can increase the apparent transit radius toward short wavelengths, roughly $0.3$--$1\,\mu\mathrm m$. For <Rayleigh scattering>-like extinction, $\sigma\propto\lambda^{-4}$ and an isothermal <atmospheric scale height> model gives $dR_p/d\ln\lambda\simeq-4H$. Larger particles instead produce a flatter, approximately grey continuum.
An optically thick <exoplanet cloud deck> can truncate the slant path through gas and flatten molecular bands in a <exoplanet transmission spectrum>, for example over $0.4$--$2.5\,\mu\mathrm m$ and the <water> band around $1.4\,\mu\mathrm m$. The observed quantity is reduced band-to-continuum radius contrast, not necessarily a low molecular abundance.
<exoplanet cloud> scattering can produce a high <geometric albedo> and distinctive optical secondary eclipses/phase curves around $0.4$--$0.9\,\mu\mathrm m$. Longitudinal <exoplanet cloud> variation can shift a reflected-light phase maximum. A spectral slope or flat spectrum alone is not a unique <exoplanet cloud> identification: particle size, gas scattering, metallicity and stellar contamination must be considered together.
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