Microsoft Digital Signature:

In Windows 98, ME and 2000 operating systems, Microsoft searches for a digital 
signature when you install any new hardware. If you have a pop-up window stating 
"Digital Signature Not Found" simply click the YES button to continue installation.
If you have a request for a '<modelname>.cat' file choose to skip it: this file is 
for the digital signature and is not used. We submit all eligible products to 
Microsoft for certification but the turnaround time is subject to many factors. 
Not having a digital signature does not affect product performance in any way.