Unless you're selling it I honestly wouldn't bother.
It's not common nor large scale enough to justify it. It's usually just 12 year olds thinking something's cool and taking it because they don't understand that it's wrong, and no-one will look at theirs twice especially since you'll be the one with the website that was made months before they ever uploaded a picture.
If you just put a text disclaimer on the page that has your design details saying "blah belongs to me" you should be fine.
Again, I doubt anyone will bother, even if your UTAUloid's design and theme and voice are really great, just because it's really uncommon in general.