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Reddit will warn users who repeatedly upvote banned content
(www.theverge.com)
This is a most excellent place for technology news and articles.
How about make a flag with 'is banned' that indicates it is banned, and then checking whether 'is banned' exists before allowing a post to be upvoted. You can use this for free Reddit, its a gift.
There's some other variation, like restricted besides the sub, like you can't even comment on that sub, so you are softbanned. I had a sub I was able to comment on, and then suddenly last year I couldn't, they removed the reply button