Never heard of 'urban whips' but your description sounds a lot like a snake whip?
Problem with pens, kubotans, etc. is length; they won't help much against a knife. A whip (if you are skilled with it) should be
a lot more helpful than those.
A snake whip won't fit into a pocket, but I was thinking maybe make it wearable around the waist, next to (just below) the belt.
But that takes work dammit.
I might get to it one of these days though... I came extremely close a couple of times to buying a snake whip for some practice.
Our neighborhood/my lifestyle/job don't call for anything like that, so it hasn't been a priority in any way. But it could be a lot of fun, to play with that thing. (And no Graham, not the kind of play you're apparently associating with whips...
)