* Stealth: Ninjas are trained to be masters of stealth and can often move about undetected. They may be particularly quiet, agile, and able to blend into their surroundings.
* Hand-to-hand combat skills: Ninjas are proficient in a variety of hand-to-hand combat techniques, including unarmed strikes, throws, and joint locks. They may also be skilled in the use of weapons, such as swords, knives, and staffs.
* Ninjutsu: Ninjas are trained in a variety of stealth and infiltration techniques, including the ability to read maps, navigate in unfamiliar territory, and use rope for rappelling and climbing. They may also know a variety of languages and disguises to help them conceal their identities.
* Physical fitness: Ninjas are typically in excellent physical condition and have a high level of endurance. They may also be proficient in a variety of sports and acrobatic maneuvers.
* Mental aptitude: Ninjas are trained to be highly intelligent and resourceful. They may be skilled in strategic thinking, problem-solving, and deception.
It is important to note that having one or more of these clues does not necessarily mean that a person is a ninja. However, if you notice a number of these clues in a person, it may be an indication that they have Ninja training.