Do not identify with what they're used for. If necessary, use a coding system. If you have doors with outside hinges, use non-removable hinge pins. Install panel doors lined with metal to resist drilling. Doors and windows on the sides and rear of a building are often inviting to the burglar because they offer concealment.
Steel reinforcing bars on doors and gratings or bars on windows offer good security.
Every exterior opening offers a potential point of entry. Do not overlook security at places like fire escapes, skylights, roof openings, air ducts, doorway transoms, loading docks, sidewalk and basement openings. Before you leave, check all potential hiding places, like bathrooms, closets and storage areas. The last thing you want to do is to lock a burglar inside. Using lights Light up all entrances with vandal-proof fixtures.