'P' - Proprietary module has been loaded.
'F' - Module has been forcibly loaded.
'S' - SMP with CPUs not designed for SMP.
'R' - User forced a module unload.
'M' - System experienced a machine check exception.
'B' - System has hit bad_page.
'U' - Userspace-defined naughtiness.
'D' - Kernel has oopsed before
'A' - ACPI table overridden.
'W' - Taint on warning.
'C' - modules from drivers/staging are loaded.
'I' - Working around severe firmware bug.
'O' - Out-of-tree module has been loaded.
'+' - Module is being loaded, probably running module_init
'-' - Module is being unloaded (state is set only after module_exit returns)
Sources:
Documentation/oops-tracing.txt
kernel/module.c
include/linux/module.h
kernel/panic.c