Keep an eye on it
What it can look like. A general, vet-reviewed example — signs vary and this is not a diagnosis. When in doubt, ask your vet. 
Crusts & scabs in dogs
Clinical name: Crusting
Dried serum or blood forming crusts and scabs, often where the dog has scratched.
Where it shows upear-margins · trunk · flanks
Typical patternEar margins, trunk and anywhere scratched.
Linked allergy typesFlea allergy · Food allergy · Environmental (atopy)
Food vs environmentalNon-specific.
What you can do
Don't pick at them; note how widespread they are for your vet.
Don't confuse it with
Other causes a vet will want to rule out: mange, ringworm, fleas.
This is educational information, not a diagnosis or treatment plan. Always see your veterinarian about your dog's health.
Related signs
Hot spotsSee your vet
A moist, red, oozing and painful patch that appears fast, with hair loss over it.
Pus-filled spotsKeep an eye on it
Small pimple-like spots with a white/yellow head.
Scratch woundsKeep an eye on it
Raw, broken skin and scratch marks from the dog's own claws.
Flaking & dandruffTrack it
Dry flakes in the coat and a dull look to the fur.