I've noticed that a lot of time gets spent in my office by people wandering around, asking if anyone has seen a certain person's birthday/bridal shower/get well/etc. card.
My solution to this is to create a small tracking device and a finder, similar to a cordless phone's 'find' feature.
the small device to the card/envelope, and keep the remote control 'finder'. When you don't know where the card is, press your remote control button, and the card will beep loudly, alerting you to which miscreant kept it on their desk for three days without signing it.
This could either be built into a card (office greeting cards are becoming more and more popular), or could be an attachable device, which can be re-used.
It could also have a built-in alarm, so that the day before someone's birthday, it could start beeping in order to make sure it gets actioned quickly at that point.