Yes, almost always signatures are only going to be relevant to civil cases, which are decided on the balance of probabilities. So all the evidence introduced is about pushing those probabilities around. A signature is neither necessary (except in some special cases) nor sufficient but it will usually be evidence for "acceptance", one of the main parts of a contract in law. A witness would shore up that piece of evidence but it rarely comes up. In most cases acceptance is not disputed because doing things you contracted to do is also pretty good evidence for acceptance and that's usual. e.g. if you're in court over a car lease, the fact you paid the first three months and drove the car is usually going to be more than enough "acceptance" for a court even if the signed document has been lost.