Michael Oliver had no choice but to caution James Maddison for removing his shirt.
There are occasions, such as this, when people will say a booking is unfair. The player, however, has accepted Michael’s position.
If Maddison merely lifted his shirt to show the message but kept it below his head, that would not be a caution.
Instead, the referee would have mentioned it in his match report for the FA to deal with. I am sure under these circumstances the FA would have warned the player and no sanction would have followed.