There are other, less-forgiving UBB boards where the "space" trick doesn't work. I think macosxhints is one of them [VBB by Jelsoft]. Somehow they must parse posts differently, in an effort to remove all extraneous "spaces". In those situations, we must use an actual (non-space) character. The non-breaking space (entered on a keyboard via option-space) does work there (inasmuch as it expands the list), but for some strange reason they choose to display non-breaking spaces as a visible square: []

In such extreme cases, i use a period... and try to hide it with white color tags: [color:white].[/color]