Antiwhoknows found an almost mint "intertwined" Thunderbolt decal. While I am ecstatic that a decal has been found that establishes conclusively what the decal looks like. I am, of course, disappointed that my idea of what the decal actually looked like was close, yet materially different. The biggest disappointment and the biggest difference is that instead of blue and red like the F-S decal, the "intertwined" is black and red like the Circle-F.
The second difference is that what looked like a thin outline on all four of the examples that I had on my Thunderbolt is actually just the edges of the decal. I lave left the outline on my master copy but changed it from a solid blue line to a dotted gray line. To accurately represent the shape of the decal, it should be cut along the inside of the dotted line.
Thanks to antiwhoknows for finding an excellent example of the third type of decal applied to Thunderbolt sirens.
Here is my master reworked to more accurately reflect an actual decal.
1970s Thunderbolt Siren Logo by
woodyrr, on Flickr
And the final design that I applied to my Thunderbolt.
Early 1970s Thunderbolt Siren Decal Artwork by
woodyrr, on Flickr