Lots of ways to do this, for example on modify avatar page:
In modifyavatar template, find
<td class="tcat">$vbphrase[edit_avatar]</td>
Down
just below that you see;
<div class="panel">
Add this to test.
<div>HELLO WORLD</div>
That will place the text HELLO WORLD dead center above where it says "Your Current Avatar"
On modify signature page, almost the same thing, except look for
<td class="tcat">$vbphrase[edit_signature]</td>
Down
just below that you see;
<div class="panel">
Add this to test.
<div>HELLO WORLD</div>
Now you know where to go, edit the div anyway you like.