Here's a thread for weird custom-made signs that defy all standards.
To start is off...
Green diamond sign, anyone?
https://www.google.com/maps/@37.716253,-79.365203,3a,21y,217.42h,86.44t/data=!3m6!1e1!3m4!1sSt9DAaqedT71N8dfgnn-wQ!2e0!7i13312!8i6656
I can't even explain this one... it's a revolutionary design...
https://www.google.com/maps/@37.748584,-79.352169,3a,15y,244.72h,84.79t/data=!3m7!1e1!3m5!1sahQfUD8ErPqPiX4srt1-ig!2e0!6s%2F%2Fgeo1.ggpht.com%2Fcbk%3Fpanoid%3DahQfUD8ErPqPiX4srt1-ig%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D100%26h%3D80%26yaw%3D19.326473%26pitch%3D0!7i13312!8i6656
(Also of note, some yellow yields signs can be seen if you pan left)
https://www.aaroads.com/forum/index.php?topic=11045.0 (https://www.aaroads.com/forum/index.php?topic=11045.0)