" Go for the Gold"
" Welcome". . .posted in different languages all over the board . . . maybe in a wordle with the Olympic rings.
Opening ceremonies could be morning message or entry tasks.
Closing ceremonies could be exit tasks or whatever you do to close the day.
"Welcome to the 2016 Academic Olympic Athlete Trials in Room______
"Mathletes Wanted for Team USA
I think you will like these themes from past olympics around the globe! I especially like
" One World- One Dream" https://olympism.wordpress.com/olympic-slogans/
Hope this helps.