When ever you post up in a guild chat the next characters together "[" "]" ( check the pictures if you didn't understand ) ,
and create more the one square with them with a text , the text get's removed and only those square's left.
When you edit , you can only see those square's
Pic 1 - with the square and text :
Pic 2 - After posting :
Pic 3 - Editing the post :
I didn't test it on the Forum's itself in order not to create spam post's .