I'm looking to buy some ECE projectors, how do I know if they are e-code? Are they that much different from DOT? Is it stamped somewhere?

Compliance info is cast into the lens and sometimes there is a sticker or stenciled info on the housing.

Ekooke is correct if you are looking at a whole headlamp. If you are looking at only the internal projector assembly, who knows but the manufacturer.

I have retroffited both Audi A6 DOT and A6 ECE. The DOT's project a beam pattern that is not shar which will give some slight glare due to light bleeding off the projector. On the other hand, the A6 ECE gives off a beam pattern that is much shaper than the A6 DOT which will have much less glare. European road signs are lighted which is why they don't need that extra light glare to be reflected onto signs while on US roads the sings are not lit which is why projector slighly bleed so they can reflect signs.