I recently added a feature where a user with the designated privilege can delete an entire encounter or patient, and all information about what was deleted and by whom is logged. This does not address individual encounter forms or prescriptions, but it could with a little more effort.
Individual chart entries are marked as ‘authorized’ if made by a practitioner. In addition practitioners may authorize entries made by non-practitioners. I believe this is OpenEMR’s way of dealing with chart signing.