Actually, most will brag about it on the webmaster tour. You can also tell by the signup page (they are all the same on NATS programs)
Once you're inside, unless they did some very custom work, you can tell once you get used to seeing them (just like with a program using MPA)
You can also tell by the webmaster referral code - which I think we all know we should be using to sign up to a sponsor, because odds are the sponsor didn't tell you about themselves.
If you need to ask & don't want to do so in public, PM me
