According to
this, it would seem that there is a sense that, for die-hard fans, attending the concert of one's chosen idol/band/singer is tantamount to entering into a competition (or doing battle, if you will) with other attendees. The goal of the competition would seem to be the attention of said performer, as well as fan cred in general.
Ringo tends to use a lot of military imagery for her tours. Expo '14 was the most obvious, with the whole band in knock-off American military uniforms. But even before that she has referred to her fans as an army, and, as we all know, used the "rising sun" design. If one views her live concerts not as mere performances, but as rallies of her most ardent supporters, Ringo's use of military imagery suddenly seems to make a lot more sense.
Which is kind of a strange thing to contemplate. On the one hand, her use of the "rising sun" flag in this context would seem to definitely be grounded in fandom and not in a particular desire to promote Japanese nationalism per se. On the other hand, it seems quite clear that she is not only well aware, but actually making use of the military/imperial connotations of that symbol.