Electronic "signature"/agreement

Last year I built a simple web-based interface for our company's annual performance reviews. This year, one of the functions they want me to add is some sort of electronic signature (so they don't have to print out and have employees sign hardcopies, and then store hardcopies).

I told them the best thing to do would probably be to purchase some sort of third-party add-on, but they aren't keen on spending a lot of money outside (hence ME building the review system rather than an actual programmer).

So, as a compromise I simply added a checkbox on the form that simply flags the "acknowledgement" field in the database. The checkbox label is some typical legalese (from our counsel) that reads: "By clicking this checkbox you acknowledge ..." etc.

After checking the box and clicking "Submit" the record is locked from further editing and is shoved in HR's "bin". It's so damn simple that I know I must be missing some important component.

I'm not looking for code-help here ... I guess I'm after "conceptual" help. Any sort of functionality that I ought to include in this little "mechanism"? I've never done that sort of acknowledgement feature before (obviously) so any suggestions are welcome.