Whats a sure sign of asthma?

None. Ther is no "sure sign" of asthma: cough, wheezing, shortness of breath, fatigue with exercise, etc can all be caused by other things. Improvement of symptoms with albuterol helps, but doesn't exclude some other diseases. Get seen, talk to your physician.
Lung function testlu. Lung function testing can significantly help in diagnosing asthma.