​​​​​It's a  visual language

With signing, the brain processes linguistic information through the eyes, and facial expressions and body movements play an important part in conveying information. It is possible to sign without using facial expressions or body movements, but doing so may give a mixed message, be confusing, or be misunderstood.

It will also look odd or unnatural to native signers.

It's not a universal language

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Each country has its own sign language, and regions have dialects, much like the many languages spoken all over the world. If you were to travel to another state and have an opportunity to sign with a person who knows ASL, you may notice that s/he will use some signs differently than you. These signs are known as “regional” signs, and you can think of them as the equivalent of an “accent.” It does not mean that people in your state are signing incorrectly. It is just a normal variation in ASL, and such regional signs add flavor to your understanding of ASL.

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It's not like Spoken English

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American Sign Language (ASL) is a distinct language with its own rules for pronunciation, word formation, and word order, and it differs from spoken English in many ways:

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For example, ASL lacks the verb "to be" and many English-style affixes, such as the suffix "-ed" used to show past tense. Instead, ASL uses words like “yesterday” or “tomorrow” to add tense.