Unless you are filtering your CI Types against users the CI Type field (by default) lists every other object in the system as well as CI objects.
In Object Designer open the Incident object and create a filter against the CI Type relationship. On the filter add a criteria of:
"Client Class" Is One Of:
Touchpaper.ClientClasses.AssetManagement.Asset (Covers Asset and all its children)
Touchpaper.ClientClasses.ConfigManagement.ConfigItem (only if you want "Configuration Item" itself listed as well as Asset etc).
Touchpaper.ClientClasses.AssetManagement.Service (Covers Service and all its children)
ITBM 7.2 onwards