While an omen can be for good or ill, only ill-omened things are ominous.  I am declaring that only high and adventurous things are important enough to be ominous.

• 10.003 and an ominous nod
• 11.008 and ominous crow.
• 14.002 for it was ominous

“omen, n.” OED Online. Oxford University Press, March 2015. Web. 11 May 2015.

“ominous, adj.” OED Online. Oxford University Press, March 2015. Web. 11 May 2015.