First of all, we need to distinguish between a “digital signature” and an “electronic signature.”
A digital signature uses a mathematical formula to implement an electronic signature that can be used to identify a unique individual.
An electronic signature is any communication that indicates an acceptance of the contract. This can be done in many ways, such as: a fax, an email, a scanned pdf, etc.
Consider an email that says “I accept the contract attached.” Courts would accept this as a signature on the contract.
My advice to clients is that you don’t need a digital signature, only an electronic signature that indicates that a specific agreement has been reached.