Turnout and getting the votes to count will be the key.
As for comparing this year to 2016--far more Democratic presence for federal and state offices in metro Atlanta (city, suburbs, and exurbs). You can even go to Hall County (73% vote for Trump) and see a few Biden signs in subdivisions.
But rural north Georgia has a sea of Trump and Perdue/Collins signs everywhere.
Does this indicate that Trump/Collins are underrepresented in polls?
It doesn't need to be a big underrepresentation for both Trump and Collins to win by a small margin.
Signs are a relatively poor indicator for election results. There's a number of reasons, but here's an illustration:
I recently was driving through a suburb in New Castle County, DE (a solidly Democratic county). In one neighborhood, there was at least fifteen Trump signs within about a half mile.
You might look at that and say "huh, that must mean Trump has undetected pockets of support here". But then, as I neared the exit to this neighborhood, I saw a man with a bunch of Trump signs under his arm as he worked on staking another sign into the ground.
