What's the difference between "signo" and "seña"?

Question

I want to look for American Sign Language classes for somebody who only speaks Spanish, but some courses use the term idioma de signos americano and others say lengua de señas americana. Are these two words interchangeable? What about the term señal? That word corresponds to "signal" in English.

Answer 1

It depends on the country you are in. In the European Spanish, a signo is defined as following:

Esp. Configuración ejecutada con una o dos manos propia de la lengua de las personas sordas o sordociegas.

Which translates to:

A movement executed with one or both hands, as part of the language of deaf or deafblind people.

This definition is marked by the dictionary as used only in Spain (the "Esp." at the beginning), whereas in the American Spanish, the word used is seña, as the definition is marked as used in America but redirects to the one mentioned before:

Am. signo (‖ configuración ejecutada con las manos).

About the word señal, it can be used as a synonym for gesto (gesture), but it is not used to speak about the sign language, as a señal or gesto could mean a movement of any part of the body and not only the hands.

In short:

• ASL = Lengua de signos americana (in Spain).
• ASL = Lengua de señas americana (in America).

Answer 2

Note: this answer is about the sign language from Spain, LSE. Each country has its own. Most of Latin American countries favor the use of "lengua de señas" instead of "lengua de signos": Venezuela has Lengua de Señas Venezolana, Argentina has Lengua de Señas Argentina, etc. For further info see here.
Regarding ASL, which is what OP is asking about, "American Sign Language" may be translated to Spanish as "Lengua de Signos Americana" or "Lengua de Señas Americana" depending on the country you're in, as explained in @Charlie's answer.

---

Spanish Sign Language is recognized by law and its official name in Spanish is Lengua de Signos Española (LSE).

You can check the law itself, or the public website for the Centro de Normalización de la LSE, or some other websites and notice that "seña" is almost never used.

In LSE, signo and seña are used for different things:

• Seña is a specific sign for a specific word concept, usually made with your hands: the gesture of touching the side of your forehead with your index finger is the seña for "think".
  • Seña personal is a specific sign that a deaf person uses as their "name" when introducing themselves: a deaf person might be called Laura, but their seña might be "a finger spiraling down from their head to their neck" because they have curly hair. When introducing themself, or when other people talk about them, they wouldn't spell out "L-A-U-R-A" but rather use their seña. To them, this is not just an alias, this is their proper name.
• Signo is every signal, movement or gesture made while talking: the movement of your lips, the expression of your face, the position of your hands and even your body. All of these elements are used when talking LSE, hence calling it lengua de signos and not lengua de señas.

Some places might use "Lengua de Señas Española" but that conveys the idea that LSE (or ASL, for all that matters) is comprised only of hand gestures, which is incorrect.