Timely also. Last night a friend told me a story about earlier this week under a bridge in NY Harbor. His 6(7?)YO asked him why some guy was staring at his watch watching the oil tankers. My buddy took a stroll over and saw that this Middle-eastern man had a stopwatch. He asked him about if the fish were biting(it's a regular local spot), and he said he wasn't fishing. So after doing that and some other discrete recon, he figured the guy was timing the transit under the bridge at a major traffic choke-point.
He went home armed with a description and plate number his son got for him and called the local police. He spoke with one he knew who said he would check it out for him.
Well, he got a call back yesterday saying that they picked those guys(he had a friend in he car) up on various infractions. But what was most interesting, they had a trunk full of surveying equipment with no apparent ties to that business.
He has also spoke to the FBI who wants him to look at some photos and whatnot. I'm being a bit vague because the authorities asked for this to be kept quiet, but I think some general info as to what might constitute 'suspicious activity' would be O.K. to share here.
Your friend did the right thing.
Now if we get "eyes and ears" everywhere we'll all be better off.