If you printed to a pdf first, but that would be a couple of extra steps which wouldn't be worth it.
Personally, I always look at these things logically. If a phrase, "digitally signed by such and such," is accepted by most pharmacies, why would a stamp make any difference." I guess it would be one more step for the patient who was trying to forge it.
I think one of the most foolproof methods would be for each doctor to have a code such as a 16 digit code which would be on your cover page. Each pharmacy would have this code and could randomly check it especially on scripts they were wary of. Unless, a patient could see the cover page (and even then 16 digits -- even harder if different types of characters) it would be hard to quickly make a mental impression), they would have no way of reproducing it. And, of course, this number could be changed quarterly.
