Fighting Spirit, though it appears to work (from checking character sheet and stats while in combat and below 50% endurance) mechanically, doesn't show up as an icon next to the character portrait when it activates, nor does it show up in combat log. I'm playing as a Barbarian, lvl 2, if that helps.

Ok, just tested it for you. It doesn't show up next to characterr portrait during combat, it probably should. It is definately working though. If you go to your character page, scroll down and then left click Fighting Spirit it will tell you it gives +7 Accuracy. Next time you go into combat just look at you characters accuracy when below 50% health it will be higher.

Yeah - I found the same thing. It appears to work, just doesn't show up anywhere outside character sheet so it's hard to know when it's kicking in.