A visitor ID system, accompanied by an ID card system, is a great security precaution to ensure that no unwanted guests enter your building. The requested URL /sourceengine/index.php was not found on this server.
A visitor ID system could be a way to allow people to enter the building without an ID card and yet still maintain the security of your building. Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
With a visitor ID system any guests will be asked to sign in, their identity checked and only then will they be given access to the building.