If an American found it, and the address was in the United States, the post office would have asked for additional appropriations for additional manpower, fuel, HR resources, and cost-of-business expenses. The teamsters would have asked for an investigation as to why the post office is allowed to compete with teamster-supported businesses, and the police unions would have demanded a police escort be sent. Hillary Clinton would have asked whether it mattered or not whether the post card was delivered, and Obama would have said that it was President Bush’s fault that the postcard was not found during the Bush presidency. Michelle would have demanded that such post cards not be delivered until the nutrition and diets of postal workers were determined to be correct. Joe Biden would want it not delivered until it could be determined that everyone could read equally, and whether or not it is written in cursive. And Eric Holder would want the card held until it was determined whether or not it could come across the U.S. boundaries with the same opportunity that other mail from other countries enjoyed.
... not to mention 47 cents postage due ;-)
And the finder would be taxed for the full value of such a rare object with all tax refunds confiscated until paid in full.