I wouldn't take that as a bad sign without further investigation.  At
times during the winter I will pop off the top of the hive (I use
telescoping tops with inner covers) and using a flashlight look down
through the hole in the inner cover.  See if you can see the cluster
of bees in the hive.  If there is no sign of any bees, then you may
want to take off the inner cover and, again using the flashlight, peer
down between the frames and see if you can see the cluster.  I prefer
this to whacking the hive, since you might really disturb the cluster
and may even knock bees off of the cluster.  Hope this helps.
Matt Ter Molen. Evanston, Illinois.  [log in to unmask]