Derrida argued that to repeat one's own signature is inherently counterfeit - it's an imitation of prior markings.
So, then, what does it mean to forge a signature? Do you forge your own signature every time you use it? Yes - you're copying the marking regarded to be your legal signature.
But, you're also operating on what the receiver's expectations of your signature are. If you don't make your signature appear identical for whatever number of reasons or excuses, you can decide to at least make it approximate to the marking that at the time it was made was performatively pronounced as your official, legal signifier.
This signifier could have been different at any other moment, but the moment you first put the pen on paper was the moment you wrote your own legal destiny with regard to your signifier. To change your signature requires jumping hoops and leaps of faith on the parts of others - particularly if your actual name remains the same. If you change it, that comes with a host of other responsibilities and potentials for false consciousness episodes.
For each signature you make, you operate under a set of contextual or practical assumptions - whether or not the recipient is familiar with your signature. The recipient could be comparing the signature via a previous contract, or your driver's license.
To change your signifier puts you at the risk of ghosting yourself, making yourself an element of undecidability. You exist, but you don't - it's all dependent on context you may have or take out of context.
(Aside - can we take context -- con/text, to mean an opposition to text? If so, is it verbal, written, dynamic or stagnant?)
Even a close approximation of your signifier might not be enough. In this rare episode not only are you in a state of ambivalent existence/nonexistence, your existence might not be recognized at all: an incredulous notary, a bad xerox copy, an unfortunate ink stain - could all render you absent.
So, who you are is basically who you appear to be to whoever is in the favored position during your communication act.