Most of them (circles, squares, diamonds triangles etc.) are in the \SilentHunterIII\data\Menu\Gui\Units folder. Sonar lines are in the \SilentHunterIII\data\Menu\Gui folder (Contline.tga, I THINK Dashline too). The ship and airplane-shaped icons at high zoom levels are in the individual ship folders \SilentHunterIII\data\Sea\shipname\shipname_shp.tg a AND \SilentHunterIII\data\Air\planename\planename_shp. tga
I don't know much about RUB, but if its JUST a matter of restoring the original .tga files (and I don't know if that's the case), there is a mod for GWX that restores the original icons that you can adapt. You would probably just need to delete the subfolders in the \Sea and \Air directories for ships that don't exist in RUB:
http://files.filefront.com/GWX_Conta.../fileinfo.html
RUB is getting a little long in the tooth. Is there any reason you're using such an old mod? I would recommend one of the newer supermods GWX or NYGM or WAC depending on your taste.