As already the 29th application by CAD Studio published in Autodesk Exchange Apps store, the AutoCAD add-on DWGsign was released recently. CADstudio DWGsign is a simple to use AutoCAD utility which watermarks your DWG drawing document with a unique, permanent and invisible silent signature containing your name or the name of your company. This add-on tool helps to protect your intellectual property as you can prove ownership of the original content in any future DWG file which is based on this signed document. Your original signature can be checked and viewed using the free DWGsign Reader application.
DWGsign does not prove an unmodified state of the original document (like digital signature does), it just proves that a particular drawing is based on your original data. Non-authorized users (even in your company) cannot remove the DWG signature. The signature remains part of the DWG file even if the DWGsign utility is not installed on a workstation. Its use is completely transparent to standard AutoCAD operations.
This is how DWGsign is used
More info on the DWGsign homepage.
See/try/buy DWGsign and other CAD Studio tools on Exchange Apps.