I personally think that bounty managers should just implement a merit requirement into their campaigns, requiring Jr members to have at least 1-2 merit to participate. Realistically Theymos isn't likely to restrict Jr. members further otherwise he would have done it already, so the bounty managers need to be the ones to curb this crap.
You trouble is is that you can't get them to do this because most don't care about quality and spammers so that's why we need to
force them to make changes. Removing signatures from Juniors is the only way to stop them from accepting them, or making a merit requirement to become a Junior. These simple things alone would clean the forum up drastically because it's becoming full of Junior-level spammers churning out on liners and they just create more and more accounts when they realise they're never going to move past Junior. Their hand needs to be forced here. I would be all for removing signatures up until Member level and that would mean you're never going to be able to earn until you've received ten merits and been here a couple of months which isn't unreasonable or a lot to ask.