I agree that it's really hard to tell unless you get to talking to someone. For me, it would probably be cloth diapers or a sling. If I see someone walking through the mall carrying their baby (sling or in-arms) instead of in a stroller or bucket, it puts a smile on my face and I start assuming things. But of course, never assume. I know alot of nursing mothers, and 95% of them are not AP. If you were to see me on the street or in the store, you might write me off because I'd be feeding my baby a bottle. You would have no idea that he's adopted and I spent 6 months trying to induce lactation. Finding out that someone co-sleeps is a huge indicator for me. Yet a good number of my adoptive parents friends sleep with their babies, and many are not what I'd consider AP.
I think like someone said, alot of it has to do with how the other parent interacts with their child. Spanking, CIO, ignoring--all those things say alot to me. Or gentle discipline, responding quickly to a crying baby, and paying attention/getting into their world--those things would tell me that this parent thinks like me. There are obviously blatent things, like a parent yelling at their children, humiliating them, treating them disrespectfully, etc. that would tell me that we wouldn't see eye-to-eye.
But again, there are just so many variables. I just think that because all moms are so unique and individual, and all are operating under their own extenuating circumstances, that there's really no way to tell just by looking or by casual conversation. There is no single model of an "AP" mother, or even more so, there is no single model of a "good mother".