Many organizations have some pomp and circumstance when getting together. Secret handshakes, code words etc. In Tim Shorts game recently we did a bit of a side quest,and met up with some members of the local thieves guild. Skord my character is a member of the guild and was also the "meat" of the local militaristic wing of the church.
When we met the thieves, Tim suggested I do a bit of world building. He asked me to describe how I let the thieves know that I was a member.
Here's the steps. Now obviously only members will know them and do it in the correct order.
1. I outstretched my arms with my wrists forward. Showing that I was a free thief.
2. I pulled back my armour exposing my heart and chest, showing that I owed allegiance to the guild.
3. I got down on my hands and knees and pulled out the dagger given to me by the guild. It has a gold filigree around the hilt. I stabbed the dagger into the ground.
Have you even came up with a secret ritual for your game?