R4 cartridges, better known in Japan as Majicon, are a major thorn in Nintendo's side. The importing and sale of these devices that allow people to play pirated DS games was ruled as illegal in Japan since 2008. Generally, Nintendo has opted for filing civil complaints or civil lawsuits against violators, but at last, it looks like the gloves have come off.
On May 30th, police arrested a 39 year old self-employed man in the Saitama prefecture. The man was charged with selling 3 R4 cartridges over the internet between February 14th and March 9th for a total of ¥7,200 (US$91.27). This marks the first such arrest of a R4 cartridge dealer in Japan, and hopefully will be a successful blow against the game piracy market for Nintendo.
Overall, there were 83 piracy-related arrests in Japan in 2011, nearly double the 45 arrests from 2010. While the majority of cases have been illegal video upload related, recent rulings and actions have shown that Japan is upping the ante and cracking down on all forms of piracy.
I'm guessing there won't be many retailers putting up Nintendo-provoking banners any more...