What does a sign indicating 'Gas' inform drivers about?

Answer: A — Availability of fuel stations

A sign indicating 'Gas' is crucial for drivers as it informs them about the availability of fuel stations in the area. This information is particularly valuable for those on longer journeys or in unfamiliar territories. The sign helps drivers locate the nearest gas stations to ensure they can refuel their vehicles before running low on fuel. In situations where drivers may be traveling through remote areas or regions with limited services, the 'Gas' sign serves as a reliable cue that fuel will be accessible ahead. The presence of such signs helps in planning travel more efficiently, as running out of fuel can lead to serious delays and safety concerns. The other options serve different functions: highway traffic signs inform about congestion or road conditions, speed limit signs indicate legal driving speeds, and notices about low fuel efficiency relate to vehicle performance rather than service availability. Thus, the primary purpose of the 'Gas' sign is to direct drivers to fuel sources, which is why the answer is sound.