A plot stamp function has been around as part of the AutoCAD LT plotting process for a long time, but its usefulness is limited by the fact that it doesn't change its size or location for different sized plots and titleblocks or borders.
Instead, I recommend creating your own plot stamp from a simple mtext object populated with fields. That way, the size and location is always consistent, whether you're plotting full size, half size, or even scale to fit.
Let's say that I want my plot stamp to include the drawing name and path, the last plot time, the user who plotted it, and the plot scale.
The first step is to start the mtext command, pick the corners, and right-click to access the edit field command.
My first field is the drawing name, which I can find under the "Document" category. I can choose the case of the field (upper/lower/sentence), and whether to show just the path, just the file name, or both, with or without the DWG extension.
Next up is plot date, which is under the "Date & Time" category. There are tons of formatting options here -- far too many to explain in a blog post, but I'm sure you get the idea.
It shows up as dashes right now, since I haven't plotted the drawing since I created the field.
For user name and plot scale I'll go to the "Plot" category.
Add some explanatory labels to the fields, and I'm done.
I plotted the drawing (you'll have to take my word for it) so that you can see what the date/time field looks like.
(Click on any of the actual plot stamp images to see them full size -- it'll be easier to read the text that way.)