[@Akayaofthemoon] Ho, hum. In the end, I never got around to that.

Part of me wants to go with something that he would have had no reason to have had at all, like an eyepatch, but given in my history, I have him as a pre-teen, Alice wouldn't remember that of him. He wasn't who he is today by any means. There is the fact that also, the only actual time Alice encounters the knave is in the last few scenes of Alice's first Wonderland adventure. The best I came up with is this, actually, which I quite like -
[img]https://i.pinimg.com/236x/b7/56/2a/b7562adf20008f624f14e9aa339fb66b--playing-card-cufflinks.jpg[/img]
As you probably know, the Knave was attending a court case. Thus, he dressed in the best clothes that a servant could - including these brass cufflinks, given to him when he ran a letter for a particular nobleman or noblewoman. However, children's clothes are not made for adult cufflinks.
So, in the commotion of the final scene, with all the cards rising up into the air (or just into a fury/a panic), I see no reason why one might not fly off, and just so happen to get caught on Alice's skirt or sleeve, or whatever. The other one would stay with him, and the two would be in separate worlds for many years, only to be reunited with its pair should he and Alison meet with both of them in possession of their respective cufflink. He would recognise it, claim it to be his, and tell her of the shoddy engraving on the back that he made with the sharp end of a dagger if sight alone wasn't enough to confirm it.