You're dealing with a wheel dummy here, but...

From what little I was able to figure out from a Google search, it sounds like the ET# has something to do with offset. And, according to a couple posts I saw, it's typical for it to be stamped on the back of the wheel.

There are a bunch of numbers/codes on the back of the wheels, but I'm fairly certain I'm seeing "ET 35" stamped on the back of one of the spokes. But, the wheels are still on the car...had to use a small mirror and flashlight to inspect, so I'm not 100% certain.

Wheels will be off the car in a few days - I'll follow up once I have a chance to inspect them more closely.