Alice has cat ears and a tail, Bob constantly worries somebody will point out Alice's oddity, but even when he brings it up, people assume it's just a costume to make her look cute.
Alice is a young girl with white hair; no one seems to find this unusual.
Someone cast a spell on the town to keep them from noticing anything unusual about the main characters in order to keep up the Masquerade.
Alternately, people with cat ears and tails have been living and passing through the community for years. At first people found them unusual, but by now they've seen so many people with cat features that they can accept Alice without looking twice.
Subverted: Everyone comments on Alice's ears and tail, even as they let other other Half Human Hybrids go without comment.
Double Subverted: Everyone notices Alice's cat ears and tail but it doesn't seem to affect their behavior.
Parodied: Alice takes her best friend, Cthu-Cthu on a tour of the town, and he decides to go on a rampage. As he does so, one of the townspeople, who's been watching the entire time, yawns and complains about how boring things are in town.
Zig Zagged: Alice starts off as a Bunny-Ears Lawyer. After Cth-Cthu's rampage, humans start pogroming hybrids. La Résistance overthrows The Spanish Inquisition; they make a law that emotionless Eldritch Abomination must be destroyed, but any hybrid who can laugh and cry and sing and dance counts as a free-born citizen, so Alice is reckoned as a person again. Then, the remnants of the Spanish Inquisition notice that Alice laughs when humans cry etc.
Averted: Anything unusual is commented upon, and noted.
The author thinks that the civilian reactions to Alice's presence would bog down the story too much.
It's meant to show just how everyday this seems.
Lampshaded: "Hey, Alice, don't you think it's strange that people never seem to notice that you have a tail?"
Exploited: Alice rides through town on a dragon twenty yards long because no one will notice.
Discussed: Alice and another character have a long heart-to-heart about how hard it is to be a catgirl in a non-catgirl world.
Conversed: "Have you ever noticed how these characters never seem to notice that there's a weird Half-Human Hybrid in their midst? What's up with that?"
Alice feels that others don't think she's special or interesting, making her doubt herself and doubt her friendships.
Or, someone actually notices whatever odd sight there is, and starts to wonder if s/he has mental problems since others don't seem to be unsettled.
Also, this trope is used to show how much self-centered people can become, to the point were anything unusual isn't poited out unless it directly affects their lives.
Reconstructed: Alice's friends reveal that they simply pretended to ignore her cat ears and tail because they wanted to be polite.