Hand signs

Ninja form hand signs during the wind-up of their techniques, and the best of them learn to do it with one hand.

In short

Ninja sign with both hands during a technique's wind-up, and every technique has its own sequence. One-handed signs are learned only by training (14 sessions alone, about 5 with a sensei) and let a ninja sign with a weapon drawn.

Two-handed signs

When a technique starts with hand signs, both hands come in from the sides to meet at the chest and snap through a series of clearly different signs: one hand stacked on the other, overlapping, side by side, one in front of the other, a raised pair, angled one way or the other. Each sign is held for a short beat, a small puff in the technique's element marks the last one, and the hands slide back out to the sides.

Every technique always signs the same sequence, and different techniques sign differently, so you can learn to tell techniques apart by their signs. The signs fit inside the cast's normal wind-up; nothing gets slower. A ninja holding a weapon lowers it to sign.

One-handed signs

A ninja can learn to sign with one hand. It is learned only by training: no scroll, trait or purchase teaches it.

Who: a ninja who knows at least one technique that uses hand signs.
Where: each session at a training post, straw training dummy or battle ring counts. Training gives one session a day.
How long: 14 sessions alone by default (about a season of regular training). With a sensei nearby (a jōnin or higher), each session counts three times, so about five sessions. The number of sessions needed is a setting (4 to 40).
Progress shows as learning one-handed signs in the health tab, with the sessions left alone and with a sensei, and at the top of the technique window.
When it's done, the ninja gets one-handed signs for good and a letter tells you.

With one-handed signs, a ninja signs while keeping the weapon drawn: the free hand forms the signs (six positions of its own, with the same snap and hold) while the other keeps the weapon ready. Without a weapon, about half of their techniques are signed one-handed for variety. Nothing else changes.