Fun fact:
This was one of many UK signs at the entrances of various hospitals during Covid, to help reduce the unnecessary spread of Covid from infectious people. Covid symptoms were usually handled differently and people with symptoms diverted to websites, phone numbers or doctors for further information, rather than a hospital emergency department unless it became one.
Evolution is a health promo and comms group working with the UK health service, the NHS.
It was commonly understood at the time.
Its still used in some areas of high infection regarding infectious illnesses like Covid.