The old FvwmTaskBar module had the StartIcon option, which, if used, would tell the taskbar to display an icon next to the start button’s title.
I’m using Fvwm3 and I’m trying to write my own taskbar following the example on the wiki, but FvwmButtons doesn’t seem to have an equivalent to this StartIcon option. The Icon option places the icon above the text, and there’s no way to specify where the icon should be. The Title option does allow you to align the text, but it keeps the text under the icon no matter how you align it.