Half-and-half scarves, if you don't know, commemorate games between clubs. They often feature the date of the game. Here are the four I own. Two are from the same game.
You'll notice the Arsenal one circumvents copyright issues.
I have some other scarves too. A vintage one from before the move to the new stadium, one that was for sale at the Wembley play-off against Bristol Rovers, and the 125-year anniversary scarf.
The Wembley one is a nice memento of a pretty horrible game.
Generally in life you only need one scarf. But these are more than that. They are a record of fandom. With the demise of the much-maligned 'Clippy' the Lion from the club badge, there are new scarves being produced for the forthcoming season. I probably will end up buying one.