1) No public mining address / no user selectable pool.
A cloud mining company that won't let you direct the hashrate to your pool of choosing and can't prove its actually mining bitcoins itself, is very likely a scam. There is no reason to hide mining address or not sign blocks. None!

2) No endorsement from any ASIC vendor.
ASIC vendors will gladly make a simple post to show the company in question is a significant customer of theirs. Its free advertisement for them and it helps their customer grow their business, so there is absolutely no reason they wouldn't. If a (cloud) mining company cant get any ASIC vendor to post such endorsement, you should assume they don't have any hardware to mine with.

7) No exit strategy.
If you can't sell your position, you can't get your money out. That's the ideal case for a ponzi and allows it to run for a  long time.


Hope this helps!