A sign tower is a mast or similar freestanding structure, often with multiple support columns, which holds up a large or highly visible sign of some kind. The sign may be a billboard, an illuminated message or logo, or some kind of illustration or sculptural object, generally for purposes of attracting attention.

One or several columns can carry the sign. Illumination is optional, and the supported element can be a sculptural object rather than a flat board.

The mast is an independent support for attracting attention. A sign attached to the face of a building does not by itself establish a separate sign tower.