I know there have been vague announcements asking to respect it but it does need something a bit stronger and more direct. A joint statement from the fans and the club read out just before kick off and shared directly via email and social media would be great. Something along the lines of this.
“We the players, staff and supporters of Middlesbrough football club would like to ask all in the stadium to please respect any player who chooses to take the knee before kick off. We do not boo the national anthem or any other pre match activity. The taking of the knee is an anti racism statement from the players and has no political affiliation. We ask that you show the same respect you expect for any other message of equality.”