What to do if I have read that in type 2 diabetes, the symptoms can be virtually non-existent, so how can you tell?

Get tested. Ask your doctor to be tested for pre-diabetes/diabetes. He/she will order you blood tests (fasting sugar, hba1c, oral glucose tolerance test) to evaluate and confirm the diagnosis.
True. Only at the advanced stages of type 2 diabetes when the pancreas has lost significant beta cell reserves ( the cells that produce insulin), that symptoms such as increased urination and weight loss can manifest. Prior to that, only through medical screening such as fasting bs or A1c that a diagnoses can be made earlier.
Diagnosing diabetes. Blood sugar testing is the gold standard. Sometimes it is also diagnosed on urine testing.