I'm going to do some work on this shortly, fixing the centring functionality should be easy - but I'm also probably going to try add in a max 100px image height and then a max of two lines of text in a very slightly smaller font size to the main post text - with a horizontal line separating them too. All just to make sure signatures don't take up too much space, and are better visually separated a little.
Social media links we'll try add better native handling eventually, where if you put it in your bio, an icon will automatically appear in your signature.
In general it'll take a few weeks to get everything polished up here yet