What about add a banner that service's admin can add in their thread? I think something like this for now:

Service's admin can add the banner in the main thread of the service and users can monitor the status. With this, admin can give users more trust and people can instantly see if that service is SCAM.
The admin that don't approve this banner (maybe, but not sure) are scammers and don't want to promote the banner because this thread alert that his service is SCAM. For the next days some service will enable this banner and we can see after some days/week the services that don't insert the banner in their thread.
Tell me what you think about it.
I like the idea, although maybe a signature is better for the service providers? Then it's displayed on all of their posts.
Thank you for feedback! Signature is a good idea but all new services uses a new bitcointalk account so they can't add the style for text format. The idea of signature is good but maybe it don't receive the attention that a banner in first message of the thread give.
I think you miss the point, your own point.
1. Can't be a centralized service.
2. Must be difficult to obtain/rare or it becomes devalued.
3. This is cryptocurrency so proof of work/guided tour seems plausible.
4. Guided tour helps raise awareness and should be a big win for players and OP.
What about something as simple as a long CA chain. Some one starts a root CA and accepts private CA CSRs, who then do the same... but this time in more secret. If your involvement get's out whomever signed your CA will revoke it.
The root/trusted CA(s) are copied around as is any CRL. Even a root CA can have public keys signed in another chain, thus validating the root. The system relies on the CAs from keeping their identities secret, save from whomever signed there CA and vice verse.
If your Ponzi is good some one at the bottom tier will approach you to get a server certificate signed and you post it on your site. Now there is an n-th level validate built right into your site, plain for anyone to see!
The person who gave you the CA gives you a hint about how to get an n-1 server cert. and so fourth.