The act of samurai tapping their swords was known as "noto," which refers to the ceremonial action of resheathing the sword after use or practice. Tapping the sword against the scabbard or other objects served several purposes:

1. Clearing Blood: In historical battles, samurai would engage in combat, and their swords would become bloodied. Tapping the sword against the scabbard or the ground helped remove any residual blood from the blade before resheathing it. This prevented the blade from rusting and ensured a clean and smooth sheathing process.
2. Alerting Presence: Tapping the sword was often done with a specific sound, which served as an audible signal to indicate the presence of the samurai. This sound could warn potential adversaries or signal comrades in battle. It added an element of intimidation and demonstrated the samurai's readiness.
3. Ritualistic and Spiritual Significance: Tapping the sword had ritualistic and spiritual connotations. It was seen as a symbolic act, representing the samurai's connection with their weapon and the importance of mindfulness and respect during the resheathing process. It was a way for the samurai to honor their sword and express gratitude for its use.
4. Practical Considerations: Tapping the sword could also serve practical purposes. It ensured that the blade was properly aligned and seated in the scabbard, preventing any potential damage or misalignment. It was a way to confirm that the sword was securely and safely sheathed.

Overall, the act of tapping the sword had both practical and symbolic significance for samurai. It represented cleanliness, readiness, respect for the sword, and served as an audible signal of the samurai's presence. It was an integral part of the ceremonial and ritualistic aspects of wielding a katana.