Water on a Bantha's Face (Earth-2356)

The Water on a Bantha's Face was a training regime that then-Jedi Knight Jiraiya adopted while training the Ame orphans. This would require the four of them to wear makeshift Bantha suits while training outside in the endless rain of Ame. This was to teach the young orphans to hone in their Force abilities and remain calm in the face of all adversities.

With this, Jiraiya also created a "Hop-In" system which was to be used in their hideout. It consisted of four wooden cards with images of a Bantha on one side and the other side was completely red. Each of their names were also printed just below the cards. Whenever one member was out of the hideout they were to turn the card onto the side with the Bantha so that the others would be aware that they were not there, and while they were in the hideout, the card should be on the red side. If one of them was gone but that person's card was still red, it would signify that he or she had been captured and something was wrong and if it should happen that a plank is turned on to the white side yet the person is in the hideout it could mean that an enemy has transformed into said person and has infiltrated the hideout. Jiraiya explained that this was done as a precaution because Ame was still war torn and politically unstable.

Source

 * https://naruto.fandom.com/wiki/Water_on_a_Frog%27s_Face_Training.