Nearctic River Otters (Lontra canadensis) deposit scat (feces), scat-jellies (mucous deposits), urine, and dark colored anal gland secretions at latrine sites. We tested responses of River Otters to removal and addition of scat to assess the role of marks. We found a 9-fold increase in River Otter urine marking along with a 5-fold increase in scat-jellies following removal of all marks from latrines, but scat deposition frequency remained constant. River Otters investigated foreign more than local scat when added to latrines. This result supports the notion that River Otters are capable of distinguishing foreign from local scent marks. The ability to recognize an unfamiliar signaler is necessary if marks function in social recognition and spacing. Our findings illustrate the potential role of olfactory signaling in the social lives of River Otters and highlight a previously un-established importance of urine and scat-jellies in intra-group communication.