Interface naming standards?

All, I'm currently working on a package that I plan on having an interface defined in. The CS docs are completely void on the subject of naming interfaces and, before I go coding my interface, I'd like to hear a bit from the list about the subject ... 1.) In the PHP manual they use iFoo (the "i" for interface) 2.) Maybe Interface_Foo? 3.) Name it whatever I please, which means there's no indication that it's an interface? I, personally, prefer putting "Interface" or some other keyword into the name of the interface so it's clear in code (ie. if ($foo instance of DB_Interface)). Thoughts? --Joe