Kirkenes 1042 km
Outside Murmansk/Му́рманск, along the M18, there is a road sign indicating the distance to Saint Petersburg/Санкт-Петерб́ург as 1382 km (Google Streetview), and another one at 1434 km (presumably another route).
This forum post contains a photo of a sign indicating 2800 km to Perth.
What is the highest ordinary distance road sign in the world? By ordinary, I mean that special signs showing far-off cities don't count; I mean only road signs part of ordinary distance signage.