check this javascript file
/usr/share/cinnamon/applets/window-list@cinnamon.org/applet.js
you should be able to edit that. i'm gonna check myself if i can find it.
if (this.metaWindow.minimized) {
title = "["+ title +"]";
} else if (this.metaWindow.tile_type == Meta.WindowTileType.TILED) {
title = "|"+ title;
}
else if (this.metaWindow.tile_type == Meta.WindowTileType.SNAPPED) {
title = "||"+ title;
}
line 406 adds [ ] around the title when the window is minimized
you should comment it out like this:
if (this.metaWindow.minimized) {
/* title = "["+ title +"]"; */
} else if (this.metaWindow.tile_type == Meta.WindowTileType.TILED) {