Well, if you are looking for gore-type trappings, there is a problem in that the wilderness is big, and therefore can't be pervasively littered with corpses. However, you can have:
Battlefields of various provenances - recent with actual corpses, or less recent with marked mass graves and environmental damage (like the trees at Gettysburg, or say Full Metal Jacket), or still less recent with undead activity at night and "red flowers that only grow where someone has bled." Of course if you go the supernatural route you can have stuff bleeding all over the place, that's kind of a gimme.
Or killing fields - Vlad the Impaler style, people impaled or crucified or hung or whatnot. You don't have to have large amounts of volume to make it effective; I seem to recall a couple of these being effective in Willow, Pirates of the Caribbean, and a Solomon Kane graphic novel. Decapitated heads placed on a city wall to show their attitude towards crime or subversives.
Or a lot of smaller clues. I am a big fan of populating random encounter charts with things other than "fights." Take a normal chart and up the encounter chance, and then have 50% of the time the encounter be "afterwards" perhaps with different time ranges. Is this owlbear scat? A single grave marker out in the middle of nowhere? A dessicated corpse in a spider web (ever popular)? Many groups are used to those kinds of things being so rare that they must be a clue specifically placed by the DM, which is a warning sign about needing to add more organic feel to your game.
Effects on people. Maybe a lot of the populace seems to be missing a limb, or an eye or ear or something. Funerals - in progress, or just a thriving trade in them. We tend to show D&D villages as having mostly healthy people, mostly intact families, appropriate gender and child roles, etc.even though they are often in border regions that get attacked by goblins or monsters a lot. Have the town guard be staffed by 12 year olds (it was good enough for the Royal Marines when fighting Napoleon) - there's not enough hale and hearty adults (and it might make PCs think twice about just killing guardsmen). And mental effects, people will be jaded (again, Full Metal Jacket is a good example) when there is a lot of kill going on.
You can go subtle instead of requiring gore in large swathes. I had my PCs staying in an abandoned barn to escape a rainstorm. They searched and searched out of boredom and found a human skull under some debris. This kicked them into high gear, and after some investigation they determined the person had hung themselves from the rafters years ago. This really got to them for some reason, and I then immediately improvised and ran a horror scenario to take advantage of their mental state, and it worked out awesomely and became a recurring element of that campaign.