My cousin and her husband look like new acquaintances in public, but are all lovey dovey and hugging each other, etc all over the place at home....so nah, you can't really tell by looking at how people behave in public. A lot of that has to do with how they were raised, past experiences, body issues, whatever it is on their mind. The more I age, the more I learn that we just can't accurately judge as well as we would like to think we can.
As for us: we're pretty affectionate, no matter where we are. To what degree depends on what we're doing, where, and why. At my son's Kung Fu class, I've noticed he won't do anything more than a squeeze on my shoulder or hand, and sitting close. I almost got my feelings hurt the first time, because that's quite standoffish for us, but he felt "funny" with PDA when we were in a room full of kids (ages 5-13). We kiss, hug, dance, tickle, play fight, all kinds of stuff in front of our children at home. Sometimes they just smile and watch, sometimes they say "ewwww" and tease us, sometimes they jump in and join (especially the tickle, wrestling, or dancing). Jeremy might make a comment about one of my doo wop songs being sugary sweet with a hint of cheese, and he gets promptly dropped for one of the kids. Out and about, we hold hands, put our arms around each other, kiss on the cheek, or peck kisses, lay our heads on each others' shoulders, etc....no making out in public, but definitely affectionate.