The biggest indication of whooping cough is the cough itself, it has a very distinct sound to it, almost like a dog barking in a lot of cases. you can google "whooping cough" and some sites have a sample of what it sounds like that you can preview.
Whooping cough is very very dangerous. the number one symptom is a cough. it will be a very distinct cough followed by a gasp of air. it will be like your struggling to breath after the cough. VERY VERY contagious and needs to be treated ASAP.
babycenter.com/0_whooping-cou…
This should answer most of your questions and has an audio file so you know what the cough sounds like.