出外國的手族....

If you are holding BN(O) or HKSAR Passport, you'll need to have a US visa(B1/B2觀光訪問簽證). When you apply for visa, you'll need to have an interview (面談)at the US Consulate and your parents are advised to be there. (只有父母或監護人可以陪同17歲以下未成年子女面談) http://chinese.hongkong.usconsulate.gov/niv_apply.html
When you enter US, they'll ask you to show financial support that you can sustain yourself while in US. Your parents does not need to sign any document.