To tar an outdoor sign, treat the wooden backing, edges, and exposed end grain with a thin tar finish while keeping lettering and high-contrast painted details clean and readable.
Tar can make an outdoor sign look old, rural, maritime, or Scandinavian. It suits carved timber signs, woodland markers, rustic shop signs, garden labels, and heritage-style boards. It is less useful on signs that need bright colours, clean hands, or sharp printed graphics.
Apply tar before final lettering if the whole board is meant to be dark, or mask the lettering if it must remain pale. Edges, hanging holes, screw holes, and the top of the sign deserve attention because water enters there first. A cloth can give a rubbed aged tone, while a brush gives more protection on rough boards.
Tar can reduce contrast if it creeps into lettering or over painted detail. Test the finish with the chosen paint or carving method before treating the final sign. For outdoor signs, the practical goal is a dark weathering surface that can be renewed without obscuring the message.