In a rather startling series of robberies in Riverside Park, thieves have apparently used a trip wire to knock down bicyclists and rob them. But the tripwire trap has a tell: A rope lying across the bike path that thieves pull taught in order to clothesline the rider. Police think the same gang also robbed a bicyclist by simply ambushing him from behind some bushes. So if you see any misplaced bits of rope, or suspicious shrubbery, probably best to avoid them.