JavaScript: A very simple way to implement electronic signature

Is there a very simple way in JS to make an electronic signature that can be handles with as much ease as check sums (hash)?

So if this is the scenario:

------------------------------------
      Locked section for client
------------------------------------
| YYYY.MM.DD  ......................|
| ........... ......................|
| Bla bla bla ......................|
| Bla bla bla Bla bla bla..Bla bla .|
| Bla bla bla Bla bla bla..Bla bla .|
| Bla bla bla Bla bla bla..Bla bla .|
| Bla bla bla Bla bla bla..Bla bla .|
| Bla bla bla ......................|
| Bla bla bla ......................|
------------------------------------
"Open" comment textfield for clients
------------------------------------
| HE34ADOV2DSASA452123 ............|

Then a decryption of HE34ADOV2DSASA452123 would give something like YYYY.MM.DD Bla bla bla where only one person with a private key (that is max 15 characters - manageable) can generate but everyone can read?

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Note it isn't a requirement to be secured evil against master minds. Just against "layman" fraud..

via Norfeldt