Following features in the correct clinical context should raise suspicion
Fever, hypothermia
Headache
Meningeal signs
Poor feeding
Irritability
Apnea
Lethargy
Seizures
Bulging fontanelle
Hypotonia
Weak cry
Hypoglycemia
Meningitis 
Upper respiratory infection 
Encephalitis
UTI
Meningoencephalitis
Sepsis
Neoplastic meningitis
Meningitis