Ruger is still young, so in the next 3-6 months I think you might start noticing a bit of a change in his demeanor regarding strangers. Your once, never hurt a fly pup, might be more willing to go head on with the creepy dude that eyeballs you a little too much. Just a heads up since you say this is your first mastiff. C C can be very territorial, and protective. But if you socialize him a lot, it shouldn't be too much of a problem. But I do think you will notice a huge difference in him soon.
We have been taking Logan to the park nearly everyday now that he has had his shots. It's a huge park. Lots of different people walking and playing. He sits and watches. I took him to the grocery store and let him watch all the people walking in and out. He does great with it... But already he is protective of his yard. He is starting to bark and growl at certain people that get to close, which I am pleased with...
So my advice is get him out and about socializing now, ( if you haven't already) cause in a few months it will probably be a lot more difficult....
And don't think something's wrong with him when he starts to be somewhat aloof with strangers, and perhaps even people he's seen a dozen times. It's just him maturing. A lot of people are quite shocked when their loveable puppy starts wanting to lunge and bark at people. It just means it's time to kick obedience training into high gear! So in all, I guess one body language that is easy to identify is the hackles up. To me that means "warning."
Oh and yes, they love using their big ol' paws to ask for everything. I think it's soo cute!
And what a nice picture