In general, the presence of animals in healthcare settings can create increased risks to patients and healthcare personnel (such as through transmission of infectious pathogens). At times, however, animals are necessary to provide accommodations for differently-abled individuals.
Signage: Approved Animal in Room
US Dept. of Justice ADA.gov Page on Service Animals: https://www.ada.gov/topics/service-animals/
US Dept. of Justice ADA.gov FAQs on Service Animals: https://www.ada.gov/resources/service-animals-faqs/