What kind of trunk mount is this?

[xc2]

New S10 owner here wondering if anyone can tell me what kind of mount this is, and most importantly, what are my trunk options?

 

[AVGeek]

Thats the OEM mount that hides under the rear plate on most models. It is designed for the OEM top trunk.

 

[Tenerester]

It's the factory mounting base for the Yamaha top box. You need nothing more.
I am guessing your dealer didnt mention anything about it when you purchased the bike.