By David Blatner in InDesignSecrets.com
How you can make InDesign skip certain pieces of text when checking spelling.
Fortunately, you can tell InDesign to ignore words as an actual property of its character formatting. That is, you can selectively turn off spell-checking for individual words or phrases. The trick is to choose No Language from the Language pop-up menu (in the Control or Character panel). Even better, make it a character style: