e-ink is used for some electronic book readers. But that’s not what I am talking about here. As electronic circuit components continue to shrink, we are fast approaching a time when we will be able to suspend tiny particles of computer memory in ink. A pen with ink loaded with these particles could be used to sign important or valuable papers. The document could contain not just a visible signature but an electronic one too, embedded in the ink.
A pen would write to the particles as they leave the pen. The signature could be authenticated with the fingerprints on the pen, the IDs of nearby gadgets such as mobile phones or other digital identifiers as well as a secure timestamp.
Ideally, the kind of memory used could only be written to once, or use something like flash ROM. If the electronic signature can’t be embedded when the pen is used to sign, then the ink would have to be made preloaded with a unique signature authenticated elsewhere as belonging to that user. The problem here of course would be that anyone could use the pen. Hybrids where some particles are pre-written and a few during the signature would also be possible.
Another minor variant would be to use magnetic particle suspension, written again as the paper is signed.