That is the rubber piece that goes up under the hand grab rail (You know the assembly for tying things down) or the grab rail your passenger holds on to. Mine fell out a little while back and it took me a while to figure where it came from. I reinstalled it with a little silicone cement.
Holy crap!!!!!!! I can't believe you posted this!!!!!!!! Mine fell off when I was washing the bike about six months ago and for the life of me I couldn't figure out where it came from. I keep it in my garage and at least 3 times a week I would take it to the bike and try to fit it between the fairing somewhere. Hahahahah. Thanks for posting this. My fear of being ridiculed prevented me from doing exactly what you did. Bravo Zulu!
Swingman Sends
I knew that perusing this board would be more productive than working on my online classes tonight. hahahaha
That is funny swingman, mine came off about a year ago two weeks after I got it. I asked the guy who owned it before me and he didn't know. I have been carrying it around for all that time in the sidecase.
And you are welcome for posting it and you not getting ridiculed.