This.
Staying under-the-radar has huge benefits, especially when carrying. I don't want to be selected, I don't want to be noticed. If someone takes a look at me, I want to look like some 60-something year old guy on his way to the grocery store. I don't want to look "old and fragile" but I don't want to look like "ready for a fight" either. I watch people but generally avoid eye contact. If eye contact is made, I smile and nod (like most harmless old guys do) or just shift my head up and to the side like I'm trying to look past the person to something in back of them.
IMO, it's a fine line - almost an art - to not be noticed but if noticed, have "something about me" that would make me unappealing to be interviewed.
In terms of clothing, I wear the same thing I always wear, which is usually the same thing most others are wearing - and never anything that could be construed as gun-guy wear. When armed in public, I remain casually aware of my concealment and perhaps unconsciously notch-up my SA just a bit higher than normal.