Reproduction:
Turn on your grid using these steps:
Select the view tab
Turn on “Show Grid” in the settings box of the view tab
Then, create a part and make it transparent.
Place a decal on the part.
Result:
Here is a rbxl file that you can open to view the bug for yourself, there’s already a part in workspace with a decal on it; just ensure you have your grid enabled. bug-repro.rbxl (2.1 MB)
This is just an effect of decals and transparent parts.
The baseplate is closer to the camera than the blue decal, so it gets rendered on top. This is not an easy problem to fix in the general case, but for your case, you can make those road signs non-transparent. Upload the signs as squares (tilt the signs 45 degrees) and tilt them back into diamonds in-game after putting them on opaque parts. It does mean you have to reupload them all, sadly.
You can also break the giant grid into many ~20x20 parts. It’ll prevent distant parts of the surface from being “on top of” your road signs.
Hey @StyxIing - so sorry we’re so late on this. If you’re still having the issue, would you mind filing another report? We’ll get to it. Huge apologies again.