as av_phile said, you can check it thru your lcd. the lcd will tell you if its receiving hi-def signal or not. my nextbase gives 1080p signal to my lcd.
if you have an lcd, set your player to give 1080i or 1080p signal thru hdmi, then depending on your lcd, you can press a button to show in the display what signal your lcd is taking. i have a lg 32lg53fr and just pressing the OK button in the remote, it will tell me what signal my player is giving.