Is the "okay" hand gesture now unacceptable to use in class?
The whole "White-power" hand sign started as a joke from 4chan or something like that. It was kind of a ploy to get the more gullible liberals all worked up for nothing. It was kind of laughable at first. However, it would seem that it's becoming more and more accepted as an actual WP symbol. I believe that some white-supremacist groups have even ended up adopting it. Still, I wouldn't worry about it as long as it doesn't seem as if you are actually pushing the agenda. 

You could always swap it for "thumbs up" or, my favorite, good ol' finger guns.