It never hurts to ask, except that one time I walked up to a car and it was only when I was a couple feet away that I saw the sole-up high-heels and the car rocking ... I tiptoed away and try to be more careful.
That was my next question: where can I get a sign that says "if the car is a-rockin', don't come a-knockin'?" We have to be prepared for all manners of emergencies, and those condoms can be used for more than carrying water.
As for the other sort of emergency, it did not occur to me that popping the hood could serve as a signal for trouble. On the other hand, an explicit signal ("call police" or "help") might provide a much needed push to passing drivers.
On another note, I wonder whether the possibility of an opportunistic robber/rapist/murdered might be better addressed by a different sort of kit. You are perhaps no less likely to encounter trouble if you're lost in a sketchy part of town. These are similar situations, and perhaps could use the same response.
Thanks for the input! I've asked the "call police" sign company how to purchase their product, and if I hear from them, I'll let you know!
Da Bing