New Moto Guzzi Door Mats Available Now
These are part GU91181003. They're supposed to prevent the threaded ends on the mirror stem tighteners from bottoming out against the handlebar. If you have installed other mirrors, such as the much better ones that are OEM on some other Moto Guzzi models (AP8104921 and AP8104922), their stem tighteners have shorter threaded ends and the spacer washers aren't needed.
If you look, you have the smaller chrome version of same part, but you still get the black ones.