Definition of Done (DoD)

The Scrum framework does not prescribe the format a Definition of Done must take.

One common approach is to write out a DoD and place it on (or close to) a task board, so it is clear to observers what "Done" on that board means.

@Ian Mitchell: Thanks (Mehdi)

Either you print it on a large paper and you place close to scoreboards so that everybody can see it, to radiate information and to be more transparent.
Or If team don't have visual workplace around and it's more technology oriented ( think JIRA, TFS etc.), part of it can be automated and integrated to your build system ( i.e code metrics analysis run before each check-ins ) and the other part can be agreed on or within the team during pair programming it could be a check list to go through among other things.