There is nothing out of the ordinary as to how your signature and posts are showing up, and it has nothing to do with there being extra line feeds after your signature.
Look at the attachment to see what I'm explaining.
Each post is inside of a table (orange outline). The table is broken up into 2 rows. Each of those rows contains 2 cells. The cells are outlined and labelled in green. Being that the row that holds cell 3 is the height that it has to be in order to hold all of the things that are inside of cell 3 (top 5 supporter graphic, avatar, info), cell 4, which is still in the same row, has to be the same height.