The signature is a hallmark of contracting, it is the pop-culture symbol for making a legally binding agreement. However, the reality of the law is a little different. Signatures are a person’s name, applied with their own hand. Signature is not one of the core pillars of a contract though. Contracts require (1) offer, (2) acceptance, (3) consideration. Lawyers generally break down “acceptance” further to indicate “mutual assent to identical terms” which means “you have to agree to/accept the same contract as the other person.” This mutual assent phase is where the term “meeting of the minds” sometimes gets thrown around. Notably absent from basic contracting: a wet ink signature in blue or black ink.
Signatures are however, a wonderful way of proving that a person is assenting/accepting something. The Restatement (Second) of Contracts explains that “[i]t is not an actor’s subjective intent to be bound, but rather the action he takes to manifest assent that binds him.” By way of example, think of going to a taco truck. You order a taco, the guy says “It’ll be 9.95,” you hand him a $10.00 and receive a taco and a nickel. No signature was done, but a contract was formed to exchange money for corn-shelled meat. The act of mutual assent in that case was your act of handing $10.00. The money leaving your hand was a clear act showing intent to be bound to the exact terms of the deal. If you had handed over a $20.00, you would have accepted the taco contract just the same.
A signature is just a universal way of saying, “I accept,” but it is not the only way to say “I accept” and it is not the only switch that needs to be flipped to form a contract. Counterexample: Someone asks you to sign a petition, you put your name on the petition and they reveal the top of the page away to show that it was actually a lease agreement to your house and you have just signed and given this petitioner the right to live there for 50 years! In no court of law would this be considered a valid signature, it was not given with mutual assent or understanding of the terms, it was not a contract. Despite the presence of a signature in wet ink, the document is invalid.
Any symbol or sign manifesting assent that shows actual, meaningful intent to be bound to the terms of the deal will suffice to form a contract. Back a few centuries and even occasionally today, you will see someone sign “X” on a line rather than writing their name. That “X” is a legally binding signature as long as the party making the letter intends to be bound. If a person signs with their nickname, if they sign with their left-hand, if they sign using red or green ink, it’s still a contract and is still binding, as long as you can show that the person intended to be bound by the term of the contract they were signing.