Have you used any artifact in Sigil?
For example I want to introduce a few of these, far far in the future tough, once the PC's become high-ups:
Maleficus Spike - http://www.d20pfsrd.com/magic-items/artifacts/minor-artifacts/maleficus-...
probably a local invention from the time of the invasion in the Hive
or
Mantis Blade - http://www.d20pfsrd.com/magic-items/artifacts/minor-artifacts/mantis-blade
Legendary blade from the times when the Hive got its name; made from a slain proxy of Apshai
Perfect Golden Lute - http://www.d20pfsrd.com/magic-items/artifacts/minor-artifacts/perfect-go...
An instrument so fine it nearly plays itself, tuned into the empyrean harmonies of the Source
Revelation Quill - http://www.d20pfsrd.com/magic-items/artifacts/minor-artifacts/revelation...
Chant is that The Peacock Lord has one, that fallen one; and PF daemons want it
Knucklebone of Fickle Fortune - http://www.d20pfsrd.com/magic-items/artifacts/minor-artifacts/knucklebon...
Remains of the gyoxchuggi?