My blood sugar 30 minutes after eating was 140 mg/dl and 143 mg/dl after two hours. is that warning sign for diabetes?

Maybe: The diagnosis of diabetes is strictly speaking a fasting blood sugar of 126 or more on at least three tests. Fasting is usually considered adequate at 10-12 hours. So while you don't meet those criteria it is worrisome that you stay high so long after a meal. I would suggest you get the fasting blood sugar and as test called a glycohemoglobin, reflecting the last two months' average BS

No : Post parandial BS of < 160 mg/dl after 2 hr is ok,ideally if you think you r @ risk of becoming diabetic you should get 90 min GTT @ lab of your choice, you can also check your HgbA1c.