An anti-theft device for use with a locomotive horn is disclosed. An angled L-shaped bracket of the anti-theft device has a horizontal portion that is connected to an anti-theft or tamper proof fastener used to attach a base of the horn to the locomotive. A vertical portion of the bracket receives a shackle portion of a padlock for connection with and locking on the bracket. A bushing is placed on the shackle portion of the padlock over the anti-theft fastener to limit slack of the padlock relative to the bracket. When assembled with the locomotive horn, the anti-theft device at least partially covers the anti-theft fastener such that access to and/or removal of at least the anti-theft fastener is substantially prevented. Thus, theft of the horn is reduced and/or prevented.