I'll go with minnick27's lip-sync advice.
Of course I don't want to annoy people with my less-than-remarkable singing voice.
I was just worried that I might be too quiet to fit in because of my partial ignorance of the song material. At some shows it can afterall be annoying for an actively participating crowd, if some just sit there in apathy... or in awe for that matter.
Seeing as the show I'll be attending is a fully seated one, I'm sure I can just lean back and enjoy the band with a smile on my face... and maybe lip-syncing some of the songs that I know.
I also find it better, when I can listen to the artists and not others singing along, but sometimes that can be fun as well and as I have never attended a Weird Al show before, I just wasn't sure what to expect.