XXX = ?

I had the pleasure last Shabbat of davening at a place where they post the current three-digit page number, using a rack with large numbered cards. Well, not an unalloyed pleasure – I was using an alternative prayer book, and had to keep resisting the impulse to turn to the “current” page. But that’s not important now. What interests me is this: when the service is over, what number should be left on the cards? Usually the last number just stays there (probably the Sabbath psalm) but why not change the last number to: 613!