These are some of the things we look for when a subject is presumed deceased, or there is a strong chance that they are deceased.
When I referenced BMI, I'm assuming high BMI due to body fat, not muscle (e.g. some body builders have super high BMIs, but virtually no fat - one reason the BMI system is a bucket of fail).
The decomposition of the lipids for a body left in-situ creates a 'ring' where plant life will not grow for some period of time. The amount of time depends on the amount of body fat decomposed into the soil, the 'washing' effects of wind, rain, and runoff, and the tolerance of any native plant species to the compounds left in the soil.
Another one is mounding. There are naturally barren areas in nature (Clear Creek in California, full of serpentinite is a good example) not caused by organic decomposition. However, the decomposition of collagen compounds will tend to attract any wind-blown dirt and dust, causing an odd accretion of 'dirt' that very roughly outlines the size and shape of the body, or what was left of the body. This tell is not obvious, and is easy erased by running water. It's 'good' for maybe a year after the disappearance.
For a body still somewhat intact in a green, vegetated areas, the off-gassing caused by decomposition can brown immediately adjacent greenery. This is similar to the effects of geological off-gassing in volcanic regions that will brown and kill nearby plants or trees. Again, this is a more short term indicator, but if someone goes missing in winter, is 'preserved', then undergoes rapid decomposition in the spring thaw, these spots can sometimes be easily seen from the air. A field of green, and a weird patch of oval or elongated brown (most common with grasses).
Finally, look for odd shaped rocks, about the size of a human head. In an arid environment, the head will dessicate fairly quickly, due to all the openings (eyes, mouth, nose, ears, spinal attachments, even the sinuses). Skin will 'leather' out, and the soft tissues of the eyes, mouth, and nose will be long gone. What you're left with is something that looks oddly like a grey, leather rock or bowling ball. A gentle tap with a stick or pole will result in a hollow 'thud', of obvious reasons.
Finally, the easiest one is just using a cadaver dog. A well-train dog AND a well-trained handler can locate remains in excess of 25-30 years old. This is incredibly challenging for the dog, because the scent profile to the dog is about the same as the scent profile a human gets from a brick - not much. At this point, the dog is really trying to sniff out bone fragments, though a few theories and studies suggest that some dogs are able to smell DNA remnants trapped within the intraosseous spaces (a similar profile to cancer sniffing dogs, being able to isolate odors of individual cell types). The latter part of this is theory, but cadaver dogs themselves exist and have been effective in the past.
Or, we just keep eyes open and look for bones sticking out of the ground.