1. A system comprising: a source device including: an interface configured to: receive an electronic document; transmit the electronic document to a dedicated signing device; and receive a signed electronic document from a dedicated signing device, the signed electronic document including the electronic document and an associated signature document including a digital image embedded with a digital watermark representing an encrypted one-way hash; a processor configured to: calculate a one-way hash of the electronic document; decode the digital watermark representing the encrypted one-way hash; decrypt the encrypted one-way hash; compare the decrypted one-way hash to the calculated one-way hash; and a dedicated signing device including: a user interface configured to receive a user input; an external interface configured to: receive an electronic document from a source device; transmit a signed electronic document to the source device, the signed electronic document including the electronic document and an associated signature document; a processor configured to: alter a characteristic of a signature document based on the user input, the signature document comprising an arbitrary digital representation; where, the processor of at least one of the source device or the dedicated signing device is further configured to: calculate a one-way hash for the electronic document; encrypt the one-way hash; and embed a digital watermark representing the encrypted one-way hash into the arbitrary digital representation.