usually if you have your profile set so that your signature shows up...then when u update it.....it will update everything....i have a feeling u didn't check show signature in ur first post and had ur sig turned off for the first post usually that isn't a problem tho.... as far as the navbar issue....
go into your admin panel...go to style - modify....for the skin u speak of..go to fonts
should be the right of the skin name...and look in ur header info, it should have html coding for the imaged navbar of which u speak...erase the <IMG> coding and put in your own text link...
but just so u know the default skin doesn't have a letter navbar, it has default buttons, usercp, home, member, search, and register if i remember correctly
that's how to fix it tho