Mike is right. The currency is valid and redeemable, but when a group of teens walks in with a $1000 bill, the bank's suspicions are aroused - not about the legitimacy of the currency, but about the way the kids acquired it.

Same with a kid walking into a bank with a hundred uncirculated silver dollars. They can be redeemed for a dollar apiece, but any honest banker [your joke here] would question whether Dad's coin collection has gone missing.

Other than the period when gold certificates could not be legally owned, all currency issued by the government of the United States is redeemable at face value for current currency or coins. But not for silver or gold, even if they are silver certificates or gold certificates. The same is true of all coinage and postage stamps - it retains its face value and has never been devalued.