.SubSubHead
From DNN2.x was supposed to affect text to be smaller than the Head class (used for module titles). QuickLinks was a special render mode of the Links module, I am not sure about the Signin but perhaps it had a compact version too.
(Thank you to Hooligannes from the DotNetNuke forum for this information.)
/* module title style used instead of Head for compact rendering by QuickLinks and Signin modules */
.SubSubHead {
font-family: Tahoma, Arial, Helvetica;
font-size: 11px;
font-weight: bold;
color: black;
}