Originally Posted by hypo

That's been in place for quite a longtime:
Message from the event girl = big prize
Exclamation from the event girl = medium prize
Nazuna = cake

Something else worth mentioning is that the big prizes are sometimes less than amazing. Some sheets will have 5k/10k gold or level 20 manyu as a big prize while also having ampies as a medium prize, so making use of the cheat sheets comes in handy.