West Ham have banned half-and-half scarves from Saturday's Premier League game with Tottenham.
The Hammers say the unusual move is part of "increased security activity" that will take place at the London derby, which kicks off at 17:30 BST.
It is one of a number of measures the club have taken "for the safety of all supporters and to prevent any fans of the away club from gaining access to home sections of the stadium".
Security staff will confiscate the half-and-half scarves - or any other item featuring the colours or crests of both clubs - before fans enter London Stadium.