I get this question from time to time. It is usually asked after a customer has experienced a problem with a DWG file from someone else that was corrupted or had a problem. They ask how can they tell if the source of their DWG files is coming from a non-Autodesk writing applications which can be source or contributor of the problem DWG files.
Here is an answer:
This is not something new. In AutoCAD since R14.01 you can set the system variable DWGCHECK to a value of 1. This will then provide an alert when you open a DWG that was last saved by a non-Autodesk application. You would not see the alert when opening a DWG file from Autodesk AutoCAD, Autodesk Revit, Autodesk Inventor or other Autodesk DWG writing applications or those using the Autodesk RealDWG. 
From the AutoCAD Help:
System Variable: DWGCHECK
Type: Integer
Saved in: Registry
Initial value: 0
Checks drawings for potential problems when opening them.
0 - If a drawing that you try to open has a potential problem, you are warned before the drawing is opened.
1 - If a drawing that you try to open has a potential problem, or if it was saved by an application other than AutoCAD or AutoCAD LT, you are warned before the drawing is opened.
2 - If a drawing that you try to open has a potential problem, you are notified on the command line.
3 - If a drawing that you try to open has a potential problem, you are notified on the command line. If the drawing has a potential problem and the drawing was saved by an application other than AutoCAD or AutoCAD LT, you are warned before the drawing is opened.
