Lewis & Short

signātōrĭus, a, um, adj. [signo], of or belonging to sealing: anulus, a seal-ring, Val. Max. 8, 14, 4; Dig. 50, 16, 74; 34, 2, 25, § 10.
Subst.: signātōrĭum, ii, n., a sealing, Alcim. Ep. 78.