A lockable cover and seal for a threaded nozzle or spout, such as a hose bib cock assembly having a passageway, an end face, an external threaded portion adjacent the end face, and anti-siphon valve in the passageway including a portion protruding outward of the end face, generally includes, in combination, a lid, a seal, a swivel arm, and a shielding cap. The lid is bell-shaped and has a central axis, an inner end including a threaded portion for threaded engagement with the threaded portion of the spout, a central cavity and an annular shoulder facing inwardly for juxtaposition to the spout end face. The seal includes an inner side for sealing against the end face of the spout and an outer side for sealing against said annular shoulder and a forward extending central recess for receiving any protruding portion of the anti-siphon valve. The swivel arm includes an inner end rotatingly attached to the outer end of the lid such that the swivel arm is rotatable about the central axis and an outer end including an eye for attaching a lock. A bell-shaped cap fits over the lid and includes an outer end wall having a central orifice therethrough for receiving the swivel arm. The cap extends forward to enclose the lid attached to the spout such that the lid is inaccessible for turning and the cap is freely rotatable about the central axis and incapable of engaging and rotating said lid.