To recreate, place a sign. Type out the text, more than one line. The text will flicker in and out. Exit the sign creation (b button on my controller) and the text completely disappears. This is happening in three different realms, in three different texture packs. (Signs in my lone solo world, however, are still working). See three attached clips

This problem is weirdly intermittent. It happened last week when a new player tried adding a sign with his name on it to our player roster tree. However, a couple of days ago I was able to put up several signs in another realm. Now, signs are not working in several different realms.