The man page for smb.conf(5) reads:
ntp signd socket directory (G)
This setting controls the location of the socket that the NTP daemon uses to communicate with Samba for signing packets.
If a non-default path is specified here, then it is also necessary to make NTP aware of the new path using the ntpsigndsocket
directive in ntp.conf.
Default: ntp signd socket directory = $prefix/run/samba/ntp_signd
On Gentoo, the default place ntp_signd turns up is instead "/var/lib/samba/ntp_signd".