I am going to machine some for mine that will be stainless and then I am going to laser engrave my skull in them.
If there was enough interest I would do Vmax or V4 or something small into the caps, but I can't laser them and make them cheap. So I would rotary engrave them if I do engrave something on them.
They will be retained with a rubber oring to keep them from slipping out. Machined from 304 stainless grade, or if I have 410 stainless in the bin I'll use that.
Todd