When you say you were not briefed, do you mean refuelling WAS taking place? If so, yes, you should have been briefed. If not, then there's really no need as the crew will check seatbelts when securing after the sign eventually does come on... it's not often, sure, but sometimes it (the sign) gets forgotten or takes longer for some reason...
Maybe some DJ crew can give you more details, but as far as I can see you'd only need to be briefed if indeed fuelling was happening...