The ContentAlert pattern involves leaving specific messages that let people know a page needs content to be added, refined, or fixed. Wikipedia does this by putting a message in a box at the top of the page.
Putting a message at the top of a page is the best way to draw peoples' attention to the ContentAlert.
Another method is to use tags or labels to indicate content that needs work. Multiple labels can be used for different types of needs (e.g., ToDo vs. FixThis). The content in need of repair can then either be found by label searches or by having a page that list all of the tagged pages (if the wiki platform supports it).
FIXMEsmiley can be used to show a image.