A signature in Bitcoin proves that someone has access to the private key of a specific Bitcoin address or wallet and could therefore sign a message.
Think of it like a letter with a wax seal: anyone can see the seal (public address), but only the person who owns the original signet ring (private key) can create the seal. The signature is like this seal—it proves that someone had access to the "signet ring" without having to show the ring itself.
Why do you need this?
To prove that you have access to an address
To authenticate messages as the owner of the private key
To verify control over the private key
A practical example: You want to prove that you have access to a specific Bitcoin address. Instead of sending coins (which incurs fees), you can sign a message with the private key. Anyone can then use the public address to verify that the signature was created with the correct private key.
Important: Only sign messages in trusted apps and never share your private key!