Using novel ionization technologies in single-particle mass spectrometry (SPMS), we analyzed the polycyclic aromatic hydrocarbons (PAHs) on individual particles from a research ship engine running on marine gasoil (MGO). We found a rather uniform PAH signature on the majority of particles. The PAH pattern is stable for all engine loads and particle sizes and differs from typical signatures of other pyrogenic and petrogenic PAH sources. Based on this observation, we conducted a field experiment and observed that the appearance of this PAH signature is associated with marine air masses. Moreover, we could detect the plume of a single ship passage at 15–20 km distance by the transient appearance of particles with the same distinct PAH profile. Consequently, we suggest the use of the specific PAH pattern as a new marker to detect and monitor ship emissions, independent of the conventional metal signatures that are not applicable for compliant fuels in emission control areas and coastal waters.