If this'll make it easier for you to decide on whether or not you'd like to order a print, I doodle something different on each and every shipping invoice that's included with the shipment. Here's one example (actual doodle on an actual invoice, scanned for your pleasure):
The character varies, but always done with a smile.
It gets better, too. I also draw something special on the front (and back!) of each envelope I mail out. Done with marker on study cardboard mailer, I never sketch anything out first, just start drawin'! The character on the front is almost the same, called "The Dreamer", he (or she) conjures up the addressee's name and address for each envelope. (Sorry, didn't get a scan or photo for this post. Maybe next time.) On the back, something unique to every single buyer. Here are two examples:
I've had people tell me that they save the envelopes, which totally makes me happy.
Now, don't you want to buy a print today? Of course you do.