If point ‘a’ is positive with respect to point ‘b’ moving a positive charge around the closed circuit from ‘a’ to ‘b’ or negative charge from b to a requires work.
The difference between the two points is the voltage polarity.
This voltage polarity is indicated by a positive sign ( + ) at point ‘a’ and negative sign ( – ) at point ‘b’.
The polarity of the voltage is also indicated by the direction of an arrow. If the arrow points from more positive to more negative potential the numerical value of the voltage has a positive sign, +6V.
If it points from a more negative to a more positive potential then the numerical value receives the minus sign, -6V. The battery symbol is often used to denote a DC voltage source but it may not always be battery. Usually the positive ( + ) and negative ( – ) signs are not shown because by convention the long end line denotes the positive terminal (the Anode) and the short end line the negative terminal (the Cathode). Thus, it is not necessary to put ( + ) and ( – )signs on the diagram.