What symptoms make you think of foodborne illness?

GI signs: Usually it is an illness with diarrhea, vomitting but also includes things like hepatitis as well.

Nausea and vomiting: Classical foodborne illness, or gastroenteritis, causes nausea, vomiting, and diarrhea. Fever, headache, and abdominal pain, may also occur. Underlying causes may be viral, bacterial, or rarely amoebic / parasitic. Symptoms usually resolve in 24 hours or less. For dehydrations concerns, severe or persistent symtoms, you should see your doctor.