Assalaamu alaykum. Suppose that I need to withdraw money frm my account and I cannot go to the bank myself, so my brother goes to the bank and copies my signature on the cheque with my permission to withdraw money, is that allowed?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

Your brother has no right to copy your signature, even if it is done with your permission, because this is considered forgery, which is prohibited in principle. The Kuwaiti Encyclopedia of Fiqh reads, "Forgery includes falsification of documents and copying the handwriting and signatures of others for the purpose of deception and lying."

The fact that you approve of it does not entail deeming it permissible, and this act involves cheating the bank.

Allah knows best.