If you have one you could check the T-numbers on the sticker on the side of the magnet. If it's difficult to see just stick your phone in there and snap a pic of it. I get cone stamps from mounted speakers this way all the time. But I always try to keep the phone at least some distance from the magnet.
T3903 Standard 8 ohm
T3904 Standard 16 ohm
T3987 Marshall OEM 16 ohm
T4416 Mesa OEM 16 ohm
T4335 Mesa OEM 8 ohm