Is there any badge for merit sources, or some plans to add this in future?
No, there's no badge for merit sources, and there's probably no plan to add this;
there's a huge difference between showing up in a "list of probable merit sources" and having a quote out there of you basically saying "I'm a merit source, come beg me for merit, complain about every merit I send, and accuse me of being part of the anti-X/pro-Y conspiracy."
The list of merit sources is also not made public, it's a voluntary position and there's no need to expose them to scrutiny, anyone paying attention would likely know who they are eventually, but the spammers are not really doing that.