March 14 Update:
**As illustrated by the latest screenshot attachment, entity hitbox as well as a blue line indicating the direction the entity is facing are shown by pressing F3+B. The creeper has its facing correctly indicated by the blue line while the arrows have scattered wrong facing directions.
March 8 Original Text:
It is easy to observe that the rotational coordinates of an arrow, resulting from teleporting using commands, are not meaningful representations of the direction the arrow is pointing at.
The attached four experimental screenshots will show how the arrow's rotational coordinates differ from the command block input as well as the rotational coordinates of the player.
The procedures of the experiment are stated as following: summon an arrow; teleport the arrow using the command block having a input including rotational coordinates; move the player ultil the player approximately faces the same direction as the arrow.
As a conclusion of these experiments, each rotational coordinates of the arrow seems to be the negative to each of the player as well as the command block input. For example, the arrow's rotation around vertical axis is +20 while the player's is -20 in degrees; the arrow's rotation around horizontal axis is -45 while the player's is +45. The rotational coordinates of the player is consistent with the command block input. Another conclusion is that the direction indicated by the rotational coordinates of an arrow does not point backwards, i.e., the tail of the arrow.