system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Signatures, how does 1. It bind me to an agreement 2. How does one prove it's actually your signature 3. What stops someone from forging my signature by being close enough and 4. What if I start writing my signature differently? is it still valid?
gpt
The primary purpose of a signature on a contract is not to establish identity, but to establish intent -- namely, a signed contract is a contract you have agreed to abide by, rather than something you're still negotiating, and the best way to signal that you agree to a contract is the sign it. 

Typically, the way your *identity* is established in contract cases -- that is, you are the person who signed the contract thereby assenting to its provisions and it wasn't some one else trying to run a con -- is that they ask you in court and you tell the truth, because it's a felony to lie. 

Therefore, any mark you make which is meant to signal assent will count as a signature, even if it is different than one you've made in the past.