anchorriver,
you can havea number of indications - those described so far are normally accompanied with a loud noise - either the enigne disintegrating, or the pax going "Whooooooooo" as the sparks emit from the tailpipe!
You can also have an engine failure without all the excitement, like a total oil loss, then engine grinds to a halt or you select HP to cutoff.
You could have continued surges. You could have acrid smell in cabin. All manner of things really. Quite often our pilots note bang and yaw, and are already correcting the yaw before they've got an idea of what the enigne is doing - and of course this is the right thing to do - fly straight and level - then put the sick engine out of it's misery.
As a previous poster put "you'll know"!
Best Regards and Safe Flying,
N1 Vibes