In the circuit diagrams, current or flux is shown by either (1) a letter designation...with an arrow indicator for the assumed direction of flow; or (2) a letter designation with double subscripts, the order of the subscripts indicating the assumed direction. The direction is thus assumed to be the flow during the positive half-cycle of the sine wave ... The single subscript, such as Is, is a convenience to designate currents in various parts of a circuit and has no directional indication, so an arrow for the direction must be associated with these. Arrows are not required with Iab, Ibc, or Icd, but are often used for added clarity and convenience. It is very important to appreciate that, in these circuit designations, the arrows do not indicate phasors. They are only assumed as directional and locational indicators.
...
Voltages can be either drops or rises. Much confusion can result by not clearly indicating which is intended or by mixing the two practices in circuit diagrams. This can be avoided by standardizing to one practice. As voltage drops are far more common throughout the power system, all voltages are shown and are always considered to be drops from a higher voltage to a lower voltage during the positive half-cycle
...
The consistent adoption of only drops throughout does not need to cause difficulties. A generator or source voltage becomes a minus drop because current flows from a lower voltage to a higher voltage . This practice does not conflict with the polarity of equipment, such as transformers, and it is consistent with fault calculations using symmetrical components.
...
Voltages (always drops) are indicated by either (1) a letter designation with double subscripts; or (2) a small plus ( + ) indicator shown at the point assumed to be at a relatively high potential. Thus, during the positive half-cycle of the sine wave, the voltage drop is indicated by the order of the two subscripts used, or from the ??+?? indicator to the opposite end of the potential difference... It is preferable to show arrows at both ends of the voltage-drop designations, to avoid possible confusion. Again, it is most important to recognize that both these designations in the circuit diagrams, especially if arrows are used, are only location and direction indicators, not phasors.