The scope of this paper is to perform a detailed spectroscopic study of the northern O-type supergiant HD 195592. We use a large sample of high quality spectra in order to investigate its multiplicity, and to probe the line profile variability. Our analysis reveals a clear spectroscopic binary signature in the profile of the HeI k 6678 line, pointing to a probable O + B system. We report on low amplitude radial velocity variations in every strong absorption line in the blue spectrum of HD 195592. These variations are ruled by two time-scales, respectively, of 5.063 and about 20 days. The former is firmly established, whilst the latter is poorly constrained. We report also on a very significant line profile variability of the Hb line, with time scales strongly related to those of the radial velocities. Our results provide significant evidence that HD 195592 is a binary system, with a period that might be the variability time-scale of about 5 days. The second time scale may be the signature of an additional star moving along a wider orbit provided its mass is low enough, even though direct evidence for the presence of a third star is still lacking. Alternatively, the second time-scale may be the signature of a variability intrinsic to the stellar wind of the primary, potentially related to the stellar rotation.