The sign says "Trucks, Stop Here, Check Brakes, Steep Hill Ahead." Ask almost anyone and they would likely tell you that this sign only applies to heavy commercial trucks equipped with air brakes. This is not the case however, the sign applies to all trucks with a licensed Gross Vehicle Weight (GVW) of more than 5,500 kg. regardless of brake system type. It could include everything from a truck tractor to a pickup pulling an RV.
Advisory signs posted at the brake check site tell drivers of vehicles equipped with hydraulic brake systems that they must check pedal pressure, brake assist, that there are no fluid leaks and that the brake drums are not overheated. Pedal pressure is tested by applying the brakes and holding them applied. The pedal must not be spongy or slowly depress. Turn the engine off, pump the brake pedal to deplete the assist, hold the pedal down and start the engine again. If assist is working properly you will feel the pedal rise slightly.
Are you towing a trailer equipped with brakes? Disconnect the vacuum lines, pull the pin on the electric switch or the lever on the surge brake to activate the breakaway brake. Try to drive ahead and the trailer wheels should lock. In addition to checking for hydraulic fluid leaks, it would be wise to check fluid levels in the master cylinder as well. Some master cylinder leaks are hidden when the brake fluid leaks into the vacuum assist chamber and is pulled into the engine and burned rather than appearing as a visible leak.