There has been much talk and comments on boards around the Japanese Internets regarding how police in Shinjuku have been stopping people who dress like some otaku - requesting a bag and pocket check with the excuse that they are looking for weapons.
This spot check is called "Shokumu Shitsumon" [職務質問] where the police ask what your occupation is and request ID. In some cases they then proceed to ask more or go through your belongings depending on how you react.

These findings have been carried out by Tantei File who also list what types of people the police do spot checks on - this list was provided by a police officer.

* People wearing camouflage trousers or jacket
* People with chains or keys (hanging off trousers)
* Looks weak (!)
* People wearing a bandanna
* People wearing leather