Farewell cards are like hot potatoes. You may know the person and want to sign the card, but resist the urge: as soon as that card is in your hands, it's your job to find the next
"I've already signed it."
"Nah, I didn't know him."
"Don't give it back to me - I didn't organise it!"
"congrats on moving into your new house".
Um. Mm. Ok. Everyone was looking at it as they got it and saying "wheres my card for finishing the laundry last weekend" and suchlike, heh.