Beacons are explicitly allowed. You can find the regulations covering them at https://www.law.cornell.edu/cfr/text/47/97.203

Relatedly, automatic control is defined at https://www.law.cornell.edu/cfr/text/47/97.3 and covers other devices as well like repeaters.

Automatic operations and beacons are allowed as long as the control operator (the ham in charge) sets them to ID properly. Permanent beacons also have a transmission power limit (20W EIRP I believe).