Padlock Symbol at Lower Left of USB hard drive Icon - What does it mean ?

Presumably the small locked padlock that appears at the lower left corner of my USB external hard drive's mounted icon when I boot into Leopard means the volume is locked in some way ????


This volume is NOT my designated Time Machine volume.


I seem to be able, as my computer's administrator, to still write to and read from this drive and the permissions look OK for it so what does this newly appearing lock icon mean and how do I get rid of it ?

Also: on the Mac's internal drive this time, Why is the finder asking for my password very time I try to move or delete files and folders from my own home documents folder when logged in normally as myself ? Don't I "own" my own home folder ?????