Strange, I’m not quite sure I see the utility of this… although no great harm, perhaps it would be better hidden behind one of the action icons below each post (Like, Link, Flag, etc… maybe a Mentions button with a number to indicate how many?)
But stranger is that this is so far below the post in question, especially with all the whitespace at the bottom of each post.
I’m not sure I believe signatures were removed in order to add this functionality – I suspect sigs were removed to reduce visual clutter, the same way signature images used to be restricted in size. But to this end, they should be able to restrict sigs to text-only (which would still provide a lot of the previous functionality, while retaining the cleaner Discourse look).