Stickers, yes - not sure if harmful, if not it would be a cool thing to observe.
To the point here some of this is a bit worrisome - Paul imitators will surely be experimenting with foreign objects in tanks and if not carefully researched could cause harm to the ceph.
Way back when, Carol found that Legos were a great toy for her bimac. Has anyone tried putting a few connected Lego pieces in a tank? Would be interesting to see whether, after disassembling them a few times, it might not try to put them back together...