*G in Y is group 3, which is ahead of 4 and 5, and in practice means you can board through the priority lane after F and J, unless there is a separate *G lane. What I have noticed though is that non *G partner status members don't necessarily get group 3 - VA gold gets you group 5, but again that has never stopped me boarding through the priority lane. SQ's signage on this is a bit weird, with *G shown against the economy queue at Changi and some outstations, but then called separately, after F and J - are you supposed to push to the front of the Y queue if you arrive at the gate after boarding commences and there is a queue? I have always just boarded through the priority lane and it's never been an issue.