I have been noticing these bright colored balls in convenience stores just behind the counter recently. After some research I discovered they are designed to throw at a would be robber to cover them in paint for easy identification. much like a paintballs effect only much larger.
Another image I found online as I didn't want to ask for a close-up shot! Anyone know what the Kanji traslates to? The Katakana says; color ball.
An action shot I found and just couldn't resist posting. The lesson here is don't shoplift from a Japanese convenience store, at least not without a raincoat you can quickly throw away as you run from the police! But really please just buy your stuff.