Standard for BGP community lists

Many ISPs publish community lists that go above-and-beyond standard route selection. Is there a standard for this? ie. I want my clients to utilize my s/rtbh setup as they see fit, for themselves. I'd also like my upstreams to do the same if necessary. Is there a consensus on which communities are used for these purposes? If so, which ones? otoh, is there such an engineer/network that has a client that they trust so much that they'd enable them to null a block for you globally, via community list? Steve