Decals. I got the OEM carbon fiber trim. It was on the car when I bought it with 124k miles, so I don't know how it was applied, specifically.
Technically they are carbon fiber with double-sided tape on the back so they will stick to the plastic dash. U want pics?

But here's a tip... The big piece on the dash, on top of the radio cluster area, had come off, because of the intense heat on the dashboard. U might wanna skip this piece, it's up to you.