Every student needs a worksheet.
Make a pair and do rock scissors paper. The loser picks one of the pictures not yet signed and does that action. The winner then guesses what they are or were doing.
For example...gestures...'Were you practicing kendo?' 'Yes, I was' 'Cool. Sign please'
Then say thank you, goodbye and make a pair. Optionally the students can switch then both can get the sign.
Continue until a few students have completed it or until a time limit has passed.
See how many signs were collected.