You may recall that when Mir was deorbited, Taco Bell deployed a 50 foot square floating bullseye in the south pacific, and said they'd serve free tacos for a day if any piece of debris hit it.

Now, the Long John Silver restaurant chain will offer free giant shrimp (that's prawns for you, Nick) for an afternoon if Spirit and Opportunity find "conclusive evidence of a former ocean" on Mars.

If NASA Finds Conclusive Evidence of an Ocean on Mars, America Eats Free Giant Shrimp

http://www.spaceref.com/news/viewpr.html?pid=13437

Since even in the optimistic case they are unlikely to prove anything beyond the existence of a lake or hydrothermal system (or whatever is likely for the hematite site), Long John Silvers is pretty safe.

On the other hand, they say they'll base their decision on whatever Steve Squires says, so perhaps if he's a kind-hearted man (and a seafood fan himself) there's some opportunity to rig the game:
"In short, MER results show that there is nothing at Gusev but a deep pile of lava flows and volcanic ashfall deposits. Nonetheless, we find conclusive evidence of a former ocean. Now if you'll excuse me, I've got a plate full of shrimp waiting for me..."

I'm all for this sort of thing. Better a bit of silly commercial PR on NASA's part than seeming aloof and disparaging of the private sector. Ditto for the LEGO "astrobots" on board. I certainly hope they have an MER toy coming out some from Mattel or the like. The Soujourner toy was pretty popular, if I remember.