The signature is not important, can be exchanged with any older one. It is written in the header of the installer, not in the compressed data and can be simply exchanged. The control file however must contain something like a pci id list with officially supported cards. This is usally only a subset of the pci ids which are specified in the fglrx kernel module. The only purpose of both files is to add a stupid watermark. A missing signature should show that you use a beta driver (or a hotfix one) - and the other watermark is that you use untested hardware. Both issues for a watermark are bullshit, because even when you use a beta driver you don't want to see it always. Nvidia just shows the beta sign when you start the X server, that's much less annoying. The 2nd case when you see a watermark mostly with new or fire pro hardware is stupid as well because the driver runs with it, otherwise you could not use it at all...