What is the correct way to indicate a NC (no connect) pin in Eagle CAD
I asked the same question of Cadsoft support only last week. I mentioned that I prefer to have a symbol on the schematic so that I know that I've properly reviewed that the pin in question can be left unconnected, the response I received was:


  We don't have an equivalent 'X' symbol in EAGLE. You could create your
  own no-DRC symbol without a footprint, if you define it as an external
  device it won't raise an error for not having a footprint. So that's a
  feasible solution.


After finding that I couldn't add a schematic symbol without a package their follow-up was:


  See the HELP pages for the ATTRIBUTE and PACKAGE. The key to defining
  a device as an external device is to create an attribute called
  EXTERNAL in the device. This will allow you to create a part that doesn't need a package. This is handled in the library.