How to accurately mark with arrows an electric circuit As I understood, we choose to mark the current with arrows going from the plus pole to the minus pole (even though we know that in reality it is the contrary).
As I'm looking at electric circuits, I notice that arrows for generators are going from the minus pole to the plus pole, and that for resistors it is the contrary (for the voltage)
How do someone determine the direction of voltage arrows in a circuit? 
Is there a physical reason to choose a direction or the other?

If, for example, I choose to use the red notation to mark my circuit, what's the reason behind this? Giving one notation for the generator, how am I supposed to mark my resistor?
 A: 
How do someone determine the direction of voltage arrows in a circuit? Is there a physical reason to choose a direction or the other?

I always use just one simple rule in all talk and drawings about electricity and circuits: Arrows point in the direction a positive charge would move. 


*

*For current arrows, this explains the direction from a positive to a negative pole / potential. 

*For voltage arrows, this would be an arrow from the positive to the negative pole (the blue one on your sketch). 

*The same would be the case when illustrating electric fields etc. 


I have seen voltage arrows defined differently in different textbooks. The keyword is: it's all about how that author defines it. Choose your definition and stick to it.
The resistor in your sketch will have a positive potential on it's left side and negative on the right side. I would here make a voltage arrow from left-to-right to be consistent with my own definition. Therefor, whenever I draw voltage arrows, I know that the positive (the higher) potential is at the arrow-start and the negative at the arrow-head. 
As Alfred says in the comments to the question, it would be much easier for you to simply skip voltage arrows and stick to the signs + and -. Only using arrows for currents, which are actual flows, is much easier to keep track of. 

even though we know that in reality it is the contrary

I wouldn't say that it is the contrary. The current flow direction depends on what type of current it is. 


*

*Yes, in most electric circuits the current is moving electrons. They have a negative charge and so move in the opposite direction of the current arrow (which points in the direction a positive charge would move).

*But for example in the electrolyte in a battery the current consists of moving ions - both positive and negative. The positive moves along the current arrow, the negative in the opposite direction. 

*In p-type semiconductors the current consists of moving "holes", which is a vacancy (an empty slot with a missing electron) that will act as a positive charge. The current then consists of moving positive charges. They move along the arrow in the same direction as it points. 
So, it depends on the situation if the actual flow of current is in the direction of the current arrow or opposite. But people had to choose something as the arrow direction, to be clear when they speak and draw. And that direction was chosen to be the direction a positive charge would move. 
A: Keep in mind that voltage does not really "flow" in a circuit. Charge is what flows in a circuit and that is what I'm sure you know is called current. Thus, it is not typically conventional to use arrows to indicate voltage (even if it is changing). If voltage is changing in a circuit we usually simply represent that as a Voltage/Time graph (output signals). Arrows in the opposite direction on voltage sources typically represents the "true" flow of electrons. The diagram may just want to emphasize that electrons actually build up on the negative terminal and are "pumped" from that side. 
A: The arrows in an electric circuit should always be marked from the positive terminal to the negative terminal of a battery. As Alfred says in the comments to the question, it would be much easier for you to simply skip voltage arrows and stick to the signs + and -. Only using arrows for currents, which are actual flows, is much easier to keep track of. If voltage is changing in a circuit we usually simply represent that as a Voltage/Time graph (output signals). Arrows in the opposite direction on voltage sources typically represents the "true" flow of electrons. The diagram may just want to emphasize that electrons actually build up on the negative terminal and are "pumped" from that side.
