steepest signed grade

i've seen discussions on here over the years about various grades & such,
but what's the steepest -signed- grade on a US highway and then on a state

i thought someone had said some us route thru NM or Arizona had 10% grades
and that was it for US routes, but i was shocked to see a "12% grade" sign a
while back on US129 right before it goes from NC into TN. It's generally
flat thru both NC and TN (though very curvy) except for this one stretch
near the dam.

there is a "25% grade" warning sign on the GA road to Apachiola Falls.

i normally don't pay much attention to signage, so the 12% on 129 sorta
shocked me, guess i'd just overlooked it before.