Levers connected to the base block of the sign are toggled down when conditions match. When the sign is powered, the track above is also switched towards the statement-assigned direction when the condition matches. When the switcher sign is powered by redstone, or by using [+train], then it will switch the track based on the statements on the sign. This can cause trains to reverse on straight rail sections. If the sign is used primarily to toggle a lever when the statement conditions match, then [-train] should be used so this does not happen.