"ominous looking" is a correct phrase in written English and can be used in a variety of contexts.
It is typically used to describe something that appears to be threatening or foreboding, giving a feeling of unease or danger. Example: The dark clouds and strong winds made for an ominous-looking sky, signaling an approaching storm.
They're a bit ominous looking perhaps, but they're just harmless, everyday birds.
When my sister got married, her fiancé was given an ominous looking pamphlet entitled, "So You're Marrying a Catholic … ".
When he arrives at an American check-point loaded with ominous looking packages (all medicines, of course), the terrified American soldiers ask him who he is.
They then hurried past ominous looking, space-suited health workers, whose instructions were to lead away anyone with a fever for isolated observation.
The morning after surgery, my doctor showed up early and passed me an ominous looking clear syringe with a red spout.
Handpresso, as it's called, is a rather ominous looking two-pound cylindrical device with a pressure gauge on its side of the sort you see in Looney Toons cartoons.
(The generals share an ominous look).
The cinematographer, Harris Savides, used old lenses and shot mostly in natural light to get a dim, somewhat ominous look.
And the ominous look ahead: "This is a time of war; the fact that it's inside our borders means it's a new kind of war".
There is a three-story house of fading red brick in Cobble Hill, Brooklyn, that gets a bit spooky looking at Halloween, with a rusty fence of iron spikes that only adds to the ominous look.
Governmental buildings, especially in the past, were designed to present a solemn, awe-inspiring, majestic, and even slightly ominous look, both in their architectural composition and their interior treatment of spaces.
