I'm looking for a visual symbol or device to denote "selection" or "extracts", suitable for depicting as a stamp or badge or similar on a document's front page to show or emphasise that what follows isn't the whole of the document itself but rather a selection of extracts from it.
For text, you can follow normal quotation patterns, eg
[...] ipsum dolor sit amet. Nunc est [...]
For images, a jagged edge, perhaps with a dashed border for what obviously wants to be a straight edge works well.
For full pages, you can put a "preview" watermark in a corner, and/or have a clear text label with the page and document number somewhere. So for example "page 14/234".