From Digimon Adventure.

The Crest of Reliability/Honesty is embodied by Joe Kido. Being the second Crest found, appearing on the ground in a cage where Etemon traps the DigiDestined. It is used to digivolve Ikkakumon into Zudomon.

 It resembles a Cross.

Here are the others:
Crest of Light 3D
Crest of Courage 3D
Crest of Knowledge 3D
Crest of Friendship 3D
Crest of Love 3D
Crest of Sincerity/Purity 3D
Crest of Hope 3D
Crest of Kindness 3D (honorific appearance)