Look for bald spots on your shingles. Hail can cause shingles to lose the granular surface material in spots.
Check the gutters. Look for granules that may have been knocked off shingles by hail. These granules often find their way to the gutter as soon as it rains.
Look for dents on your shingles. Dents and dings on shingles are an indicator of hail damage, especially if they show through to the back of the shingle.
Touch your shingles. Shingles with hail damage may be softer than those without hail damage.
Inspect metal parts on the roof. If the hail was able to damage gutters and metal vents, your roof was likely damaged as well.