The acid test for me is the transparency, or lack of it, about how they are actually supposed to be making big enough profits to pay such high roi without being a ponzi. If it's vague "arbitrage" or magic miners that you can't check, then it's red flag for me.
There are many investments that are high yield in the fiat world, but the reverse of secrecy about method of earning applies. If you are offering +++% then any prospective investor would expect to be told exactly what you were doing, and how you were doing it and nobody else could. Then you take an informed risk and make your choice. The risk with a ponzi is different, calculating or hoping to get in and out early, second guessing a criminal's attention span.
Some people make a living at this and usually shill the threads where they are involved and this place seems to be full of them.
This site ticks all the classic ponzi boxes:
"Trial period" or private investors only before the brand new website appears.
Generic UI.
Magic formula.
Anonymity.
Meaningless content.
HYIP sites links.
Referral program.
Incentive to lock in for longer term.
http://expertbtc.com/ 
