Euro vi green sticker/plate

As said, L is for the austrian network, certain routes are only open to “quiet trucks” 24/7. Salzburg-worgl, the scenic route missing the big german corner for example.

And for other routes you can only drive at night, 22:00-5:00, with a “L” plated truck.

No L plate means no night driving for a lot of motorways, soon to be all.