If you are providing a paper copy of a drawing to an external person or organization, you can't really control what happens to that paper. Usually, you provide the copy because you are ordering that item. Supplier and purchasing controls fit in here, including receiving inspection. Often, the paper copy is associated with a purchase order, which becomes a record. It is up to you if and how you want to stamp the copy.
When you receive a drawing from a customer, you should have a process for protecting that customer property. You can stamp the documents as you see fit. However, the stamping process needs to fit in with a larger set of controls.
For every stamp that you use, you need to define what that stamp means. Employees then train to the document that explains what the stamps mean. Since you won't be training external entities to your documents, using stamps on documents sent to your suppliers may not be useful.
I agree with Jim regarding the revisions numbers and letters. In my experience, when a drawing is in the R&D phase, the revisions are numeric, and the approval consists of one engineering signature. When the drawing is transferred to production, it revises to an alpha level revision. This conversion to alpha takes place even if the dimensions and tolerances are the same. The alpha revision indicates that the drawing is ready for production and has had a cross-functional approval. (Something that did not occur during the R&D phase.)