Premiere Elements (but not Premiere Pro) displays visual icons for each effect. You will need to provide icons for your effects, or else an empty black icon will be shown for your effects, or even worse behavior in Premiere Elements 8.
The icons are 60x45 PNG files, and are placed here:
[Program Files]AdobeAdobe Premiere Elements [version]Plug-inCommonEffectPreviews
The filename should be the match name of the effect, which you specify in the PiPL Resources, prefixed with “AE.” So if the match name was “MatchName”, then the filename should be “AE.MatchName.png”