What are the symptoms of Diabetes?

In my family, diabetes is hereditary. My mom, grandpa, great uncle, and great grandpa have it.

Im borderline diabetic because of the heredity, but im not fully diabetic because i eat healthy and excercise, but im overwieght. :(

Im not diabetic, but im just wondering, what are the symptoms of diabetes, and also how can you prevent them besides diet and excercise, unless thats the only way.