Reading glasses are almost always a sign of Presobia, a condition that causes you to need reading glasses even if you are nearsighted. This is caused by getting older, not diabetes. Diabetes is responsible for retinopathy which has very different symptoms and is very dangerous. If you are diabetic you should see your eye doctor once a year PERIOD, no if, ands, or buts!!
So to answer your question, its probably not a sign or symptom of something more serious, simply a sign that you are getting older.