Besides the obvious:
- Touch interfaces (especially mobile ones)
- A sign saying "You can scroll here you know!"
This for a desktop application.
Besides the obvious...
An indication that what is on screen is not the complete content. For example:
Text stops mid sentence
A border box shows no bottom but has the left and right edges stopping at the bottom. Even more emphasized if they have drop shadows.
Text or lists that cut off the bottom half of a line.
Pictures cut in half
Long text which has a contents list at the top but only a subset of which is visible - and no other way of 'paging'. Faqs are an example of this.
Basic mobile phones use a section indicator which is not interactive but just shows that for this page you are on section 1 of 4 for example.
Familiarity and similarity to other pages where the user has become accustomed to a page having certain content - in particular 'end markers'. An example of this might be looking for a submit button at the bottom of a form, or the comment field at the bottom of a blog entry. The textual footer links on many sites are also common expected end markers.
A list of items with a scrollbar often also cuts off items or rows of text when they extend beyond the visible area - enhancing the effect. A web browser does it too, though the fold could be placed so it doesn't cut any by pure coincidence.
WP7 addressed this by indicating possible swipe actions by cutting off content and titles and also having entire screens intrude a little on their neighbours.
The home screen actually has (or had) an arrow icon besides the peculiar empty space on the right-hand side that tried to signal that there was more to see on the right. Also, the tiles are cut below the vertical fold as well.