I can give you an n=1; I have been detained by police for walking around in a suburb.
I was 18 and in community college. I couldn't drive so relied on rides to and from. Sometimes I had several hours between classes so initially I went for long walks since there wasn't much else to do. There was a quiet neighborhood across the street so I usually walked around there.
That stopped after a cop drove up to me and ordered me to state my business. "What are you doing here?" he asked.
"I'm just walking around," I said. "I-"
"_Why_?" he asked, looking incredulous, like I had just said I had been trying to skateboard on the back of a turtle.
Apparently he had been called because of my "suspicious activity": there were some cool rocks on the shoulder of the road that I had stopped and fussed over. (And probably pocketed, because hey, cool rocks)
There's your reasonable suspicion: college kid picking up interesting stones from the public shoulder of a road.
If Mr. Policeman says you look suspicious, guess who's getting stopped?