You don't say what browser you are using ?
In IE9 right click a icon >customize title widths & choose from long titles, short titles or icons only , whatever you choose is global ( will be applied to to all icons)
In Firefox, Chrome & Opera you can right click the icon & choose properties or edit for Chrome & delete the name
Opera also has the option of globally selecting the behaviour in the Appearance Menu under the tool bar tab>select the bookmarks toolbar >Style & choose from images only, text only, images & text below and images & text on right.
edited In Opera you can right click the bookmarks bar & set the style there.