In Physics, + and - signs are often used as indicators of a vector's direction. The convention that up is + and down is - is assumed and if an acceleration is directed downward, it is referred to as a negative acceleration. Similarly, the convention that rightward is positive and leftward is negative is assumed and a force that is directed leftward is referred to as a negative force. Thus, careful students of Physics become accustomed of a + and - sign referring to a direction. Work is often referred to as being + or -. But don't be fooled! Work is not a vector quantity, but a scalar quantity. This begs the question as to why is a + or - sign used when expressing work? Work that is positive (+) is the result of a force that contributes energy to an object as it does work upon it. Work that is negative (-) is work that removes energy from an object as it does work upon it. But positive and negative work is NOT a sign that work is a vector.