Apollo 11 crew quizzed by US Customs

So, what exactly were the US customs looking for when the lads splashed down in the Pacific? Steven, who is clearly not a man to waste words, has offered the following:

I believe some of the crew secreted US postage stamps which they franked and sold when they returned to earth.

Short and sweet, just the way we like 'em. Of course, all of this is assuming that they actually went to the moon at all. I mean, if you look at the lighting on that photo, it's clearly been shot in a Hollywood back lot [insert conspiracy theories as required]