Sinclair Gas Wooden Signs

Picked up this sign and another one just like it at a weekend sale this month. The lady I bought it from said her dad had stashed them in their attic many, many years ago. She mentioned it was originally housed in metal sidewalk frame, but tossed it due to the excessive rust. She claimed it was disintegrating on her. The signs were removed from this frail frame and were oriented back to back. Has anyone ever seen wooden Sinclair sign like this? What time period would something like this have been used? I'm thinking late 40s or early 50s, but that's a guess. I love the patina on them! Any help on this would great, thanks!