why does an in-tree loadable module taint the kernel

[jim.cromie at gmail.com]

serio_raw is apparently tainting the kernel when its modprobed.
why ?  other modules load properly, no code changes to this module

bash-5.1# dmesg | grep -i taint
[    6.517150] serio_raw: module verification failed: signature and/or
required key missing - tainting kernel
[    7.449072] CPU: 0 PID: 203 Comm: systemd-udevd Tainted: G
  E     5.13.0-rc6-lm1-00004-g28dc6f490a7f #106