Last time I checked in at Perth, they had a sign up saying the line was for Qantas Club, Business Class, Platinum, and One World Emerald. The queue was shorter at economy so I checked in there, and was told very politely that as a silver I was allowed to checkin at business.
I've also been confused by the scrolling signs at Sydney, but I've checked in there a few times without any problems (normally I use quickcheck though).