Legal Question in Consumer Law in California

No. A basic email would not qualify as a signature. In recent years most states and the federal government have passed laws on electronic signatures and emails that conform to those laws may constitute such a signature, just as clicking "agree" on the license when you download software updates constitutes an electronic signature. That said, however, very few contracts need to be signed in order to be binding. The contract is the agreement between the parties, not the document, whether paper or electronic. So for most contracts and proof of their terms, signed or even written, or not, is enough. Even if the contract is one that must be in writing, such as one that you find you have to sue to enforce more than two years after it is breached, the righting does not have to be signed if there is proof that the party you want to hold to it agreed to it.