Works on both Survival and Creative modes
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What I found is that when I try to place a sign on a fence block, something causes me to be unable to add text to the sign. Its not only my game, but also all the players I've told about this. Placing a sign on any other block works just fine, but when I place a sign on any face of a fence block, signs don't work correctly.

To replicate this glitch, open up a Singleplayer OR Multiplayer world and place a piece of fence on the ground. Then take out a sign and try to put one on the fence. As you'll be able to see, the sign is placed without text.

I was able to find a YouTube video showing this glitch here: https://www.youtube.com/watch?v=GUVYwJmZtrQ