A web app I'm writing singles out individual characters found on a traditional keyboard. I have a very limited area in which the character can be displayed (which is basically the width of a W character in the font I'm using) meaning I can't display the word "space" or "blank space".

How can I best display the blank space character?

I've tried a couple of options, but I'm not sure if these would just lead to confusion:

• Using underline. This looks a bit too similar to the underscore character.
• The space symbol (␠ (␠)). I didn't even know this existed until I started looking for answers to this question myself, so I'm not sure if this is widely recognised.
• A faint bottom border in a different colour.
• A block character (█ (█)) like those used in a terminal to represent the cursor.
• A blank space with no style applied.

I suppose it's worth noting that this is purely for display purposes; the user has no interaction with the character other than acknowledging it's there when reading through the page (so I'm not asking about What character can I use to represent the space bar?).