atetsade, first of all it does not say that these two items must be met by the same act. For example, you might identify the current revision status on the document itself. However, you might identify changes (on this document) are identified through training (this could be the best way for changes in the steps of a work instruction).
Different documents can use different means. As you stated, perhaps on drawings you use a letter to designate the rev level (common practice). On procedures you use a dash followed by the rev number.
The key point here is that anyone using the document knows what revision level they need and if there is a change, they must know what the change was. They should not have to disect the document, and compare it to the old document, to find out what changed.
So the two questions are:
Is the document current?
How do I know what changed?
Hope that helps.