Alter Aeon Online Help

Keywords are:  'blacklist mark'

If you are really unworthy of a god, or do something truly awful, your god
can chose to brand you with a black mark and disown you as a follower.

You must remove the black mark before you can worship another god.  To do
that, you must have another god remove it.  This is expensive, and often
costs the god removing the mark a lot of power.