Signature+ is gone, but you can still nominate for it if you're exclusive (the option also appears for indies, but has no effect apparently), for two things to happen: if accepted into S+, the file will be mirrored on Getty; and, royalties paid out for the file in subscription will be $2.50 rather than $0.75, even though there won't be a difference in pricing for credit purchases.
We can all have our own views about the value of mirroring to Getty, but the subscription royalty structure seems bizarre under the new system. A well-favoured contributor who gets a lot of acceptances to S+ will be making more than 3 times as much on subscription downloads, even though the collection no longer exists from buyer perspective. There's no value added really, just iStock deciding which picture they want to reward more over others.
I don't know what to make of it, except that it probably won't last. Wouldn't a single, higher commission across the board be fairer?