Callouts’ placement directly suggest their level of importance. Use callouts in context and in proximity to the content it relates to. The goal is to create a visual hierarchy and relationship between the different elements on the screen.
Colors and icons also help emphasize the purpose of callouts: green (success), blue (information), orange (warning) and red (error). Content should determine which callout variation to choose.
The structure of a callout is determined by its content and intent. Some callouts are strictly informative while others require users to act upon them.
Callouts are static or interactive. Interactive callouts have a call-to action and need to be actively acknowledged by users. They can direct users through a page flow or trigger a slider (information panel). Static callouts simply disappear when they’re no longer relevant.
Note: These images are from the iOS Callouts — Android does not have the chevron.