This bug occured on a local server but persisted when trasferring the world to a single player game. All signs had become invisible. You can see their bounding box but the textures are no longer rendering or something. Everything seemed fine when logging out and shutting down the application in the session prior to when the bug appeared.

In the screenshot I placed a sign on the stone slab and only the bounding box is visible.

I saw a "Resolved" variant of this in one of the 1.13 snapshots but wasn't sure if or how to reopen, so i made a 1.13 one. Sorry if incorrect.