How can I eliminate certain sites in Safari searches by default?

I've looked around and can't find an answer. I hate that I have to add -reddit and -quora in every search I do to avoid these annoying and hit-hogging sites. I just don't want results that start with guesses and opinions from these sites.

Surely Safari offers a way to set search parameters to leave out certain sites? I'd rather "opt in" with a +reddit/+quora or just go there.