You can't really say it, can you?
No, it is more appropriate to say "communicate in sign language" as sign language is a visual-gestural language and not spoken.
To sign "children" in American Sign Language, you can use the sign by crossing your arms in front of you while wiggling your fingers on both hands.
In American Sign Language, you can sign "outside" by using the index finger of both hands to point outward from your body in the direction of where you are referring to outside. This can also be accompanied by a facial expression and body language that conveys the idea of being outdoors.
In American Sign Language (ASL), you can sign "garland" by signing the letter G, then moving your hands in a twisting motion to represent the string of items hanging.
In American Sign Language, you can sign "WHEN YOU BORN?" to ask someone when they were born.
To sign "Are you happy?" in American Sign Language, you would sign: YOU HAPPY? with raised eyebrows.
You sign it.
In American Sign Language (ASL), you can sign "I can understand" by signing I-KNOW, UNDERSTAND.
In American Sign Language (ASL), you can sign "I know" by pointing to your head with your index finger.
nothing offical outside of signers and interpreters.
A sign language teacher is commonly referred to as a "sign language instructor" or "ASL (American Sign Language) teacher."
To sign "Are you mad at me?" in American Sign Language, you would sign: "YOU MAD ME?" while raising your eyebrows and looking concerned.