The _ probably has a meaning too, but it simply was not part of the user links, which are underlined by default and look exactly the same as an underscore.
Like this_ (does not work for people who have hyperlink underlining turned off, of course)
Huh? Even IE allows to control this from within its options
Of course, using a stylesheet override accomplishes the same (and much more) but just for this...
btw, the _ at the end is a "feature" of most browsers .
it's actually included in their licence name, but doesn't get taken into process when using a-styles . unless its got an alpha-numerical character after it