I'm looking into these two headphones so I'm wondering if you can tell which one is 250 ohms and which one is 600 ohms?
Does it actually say on the headphones itself? (says if you're buying one without the original box)
If it list "600" on the headphone's jack, then it's a 600-Ohm.
Truth is the 250-Ohm and 600-Ohm sound almost exactly the same (almost).
Just to reiterate what pp312 said, please find the photo of my DT880 Premium (32Ohm). My T90 with 250 Ohm has NO marking at all.
I read your post pp312 - oops no I didn't April's fool.
For what it's worth, if you want to be extra sure, any cheapo multimeter should be able to read the resistance. If it's in the 250 ohm range measuring from tip (or ring) to sleeve of the jack, i.e. between left or right channel and ground, then it's the 250 ohm version.