Need "carat" for currently active Superfish menu item
Your best bet would be to just use CSS.  You can create that effect using absolutely positioned pseudo elements with some border tricks.  For example:

.sf-menu li {
  position: relative;
}

.sf-hover:after, 
.active-trail:after {
  content: "";
  display: block;
  position: absolute;
  width: 100%;
  height: 20px;
  border-left: 20px solid transparent;
  border-right: 20px solid transparent;
  border-top: 20px solid #369;
}