Do I need to sign the word 'YOU' first?
Not necessarily! In ASL, if you are looking directly at someone and asking them a question, the 'you' is already implied by your eye contact and body orientation. Just signing 'SIGN' with raised eyebrows is perfectly clear.
Why do I have to raise my eyebrows?
In American Sign Language, raised eyebrows act as the grammatical marker for yes/no questions. If you keep your face neutral, the person might think you are just making a statement or bringing up the topic of signing.
Does asking 'Do you sign?' mean the same thing as asking 'Are you Deaf?'
No, they are different questions. 'Do you sign?' simply asks if the person knows and uses sign language, which applies to hearing people, interpreters, and students as well. To ask if someone is Deaf, you would use the specific sign for 'DEAF'.