Somebody Else's Problem field

The Somebody Else's Problem field, or SEP field, is a device from The Hitchhiker's Guide to the Galaxy that cloaks someone or something by making everyone regard whoever or whatever is cloaked as somebody else's problem. They duly ignore the cloaked object. The SEP effect works best if the cloaked object is especially improbable; thus, for example, you can make whole mountains disappear simply by painting them pink and erecting a small SEP field generator.

In the PPC, agents in disguise are normally hidden from the view of canon characters by the canon itself, which recognizes a friendly force when it sees one. This cloaking effect works best on active protectors, such as assassins. However, they are still vulnerable to being seen by Sues and other OCs if they're not careful enough, which can be a big problem if they're disguised as something canonically hostile and/or out of place for the current setting, such as orcs in Bree.

Therefore, to cover all the bases, this handy gadget can be found in flash patches and See-Through Devices. It can also be activated in a PPC TARDIS if the chameleon circuits go haywire. It is not known if the SEP field turns the TARDIS pink.

The Mary Sue Factory used an SEP field to conceal itself, but was still discovered; it's possible the League of Mary Sue Factories still uses SEP fields for a similar purpose.

Breaking the SEP Field
The SEP field will cloak an agent from being detected by original characters in a fic unless the agent draws attention to himself somehow, making himself the OC's problem. Talking won't do it, but a loud noise might, and interacting with the character definitely will.

An SEP field may be less effective on a character that knows of the PPC's existence, or else is omniscient in some form.

A SEP field does not protect agents from being affected by events in the continuum. For example, it would stop a Gary Stu from seeing PPC agents and shooting them; but it would not protect the same agents from being hit by a stray arrow during a battle, being drenched during a rainstorm, or being buried inside a collapsing building during an earthquake.

Use in Missions
Usually, the SEP field works so well that nobody even mentions its existence. It is a credit to the DoSAT that most notable incidents involving SEP fields are the few times when they fail.
 * "Sue Be Nimble, Sue Be Fast, the PPC’s Coming to Kick Your – " (The Lord of the Rings), Agents Manx and Shadow (DF) with Agents X and Arya Dragon
 * A Sue notices the agents and points them out to the canons.
 * "Melodicas, Pain, and Oxford Commas" (Gorillaz) (NSFW), Agents Laburnum and Foxglove (DMS)
 * The agents laugh hysterically and knock things over loudly enough to attract attention.