In a tasks list, you can organize priorities by defining an order between tasks.
You can also use sections to define priorities inside the list such as top priority, pending and non-urgent. 

On a board view you can also use sections and move tasks from a section's column to another according to their priority status e.g. P1 P2 and P3.

You can also use subjects such as High (red) Mid (yellow) Low (green) to color code priorities on top of organizing tasks between them and in sections (i.e. columns in boards/ separators in lists).

Examples in a board view:

The task is multi-homed on different Subjects. One of them represents a priority level.

Another nice and simple possibility is to add emojis to tasks labels :

How to add an emoji :

From the task label position you'd like to insert an emoji, press either of these keyboard shortcuts:

An emoji picker will appear on screen over the text field. Click any emoji to insert it