App to display IP address in menu bar?
This small application runs in the background and shows the current IP
  dddress of your Mac in the menu bar. There are options available to
  customize the appearance of the menu entry. The IP dddress is updated
  regulary. Switch on the Router option if you are behind a router or
  gateway. You can still see your local IP address in the menu.


https://www.monkeybreadsoftware.de/Software/IPinmenubar.shtml


  Do you need your computers IP address often? If so, IPMenulet is
  likely the quickest way to have the number handy all the time, it’s a
  free and simple menu item that displays your current external IP
  address in the Mac OS X menu bar, there’s no other frills or features.
  
  You can download IPMenulet now (direct .dmg download – link changed
  visit dev site instead) or visit the developers website here for more
  information and to view the simple tools source code.


http://osxdaily.com/2011/06/30/show-ip-address-menu-bar-mac/

And the associated Google Search :

https://www.google.fr/search?client=safari&amp;rls=en&amp;q=ip+menubar+os+x&amp;ie=UTF-8&amp;oe=UTF-8&amp;gfe_rd=cr&amp;ei=N-0WVve4KMe7bpKHpogO