This brings up a nice story. A few years back, I was getting on a plane that was heading for England (I was heading to Spain) and I saw Duff McKagan (oh, my...bassist from GNR and Velvet Revolver. Yes, I understand I am in a minority of visually recognizing and knowing the names of a musician that is not the lead singer--but, I am writing to a MLP forum, so you are likely likeminded individuals.
I told my friend, who he was and I wanted to say hello and get an autograph. However, he was wearing a Velvet Revolver t-shirt. I thought to myself, that is way too obvious, it couldn't be him--although nobody, including my friend knew who he was even after I mentioned his name. A big-time rockstar wouldn't wear his t-shirt, it would draw too much attention and I thought musicians wouldn't broadcast that they are fans of themselves. Well, when I got back to the dungeon (coach in the way back), we looked up pictures of him to compare the tatoos and we did verify it was him. However, we didn't want to draw attention to him, now that everyone is locked on the same international flight, so we decided to wait till we land to say that we are big fans. However, when first class deboarded, he was long-gone by the time we got off the plane and we missed our opportunity.
With that being said, I see nothing wrong with putting up a flag to broadcast their association. It can not only trick your fans to seconding guessing who you are, but you also get the word out of the band and you can say you are proud of your recent accomplishments.