That sight is a gas price sign reading below $2. Now, there's a caveat, this number comes with a car wash discount. But, even without it, gas at many of these locations along page has dropped to just $2.15 a gallon. There are very few places anywhere where it's lower.
According to GasBuddy.com, which tracks these numbers, the state of Missouri has the lowest average price for gasoline in the US at $2.39 per gallon. But, the St. Louis average falls lower than that at just $2.34. The average price here in St. Louis hasn't been that low in five years when fuel prices were recovering from a free fall during the great recession.
As for these $2.15 prices, they are prevalent in the Maryland Heights and Overland areas right now, and drop a penny lower in a couple of spots.