Howdy!
In plenty of games the devs have hidden easter eggs and usually in plain sight.
Due to this it might be something fun and refreshing to have an entire jam orientated towards it.
Daring to say... are you able to hide things in plain sight?
Even if you hide something very well, make sure to have an experience for the users.
Needless to say that all participants (and others) will be able to play each others creation.

Just to clarify, this also has something hidden in plain sight.
As did my initial announcement in the Discord server.
Meaning that it can be as simple as this!

Rules & tips:
A team can be of any size as long as you can manage it and yes anyone can be a participant.
Want to participate, but don't have enough time? You can just join for a couple of hours. 
Reason for this game jam is to spark creativity in the community by thinking about easter eggs and how to hide them in plain sight.

Extra:
You can work with your team in a designated discord server with others if you want at: https://discord.gg/6TdJdYDY