To add a border make a new layer press CTRL+A to select the whole canvas then go to Edit>stroke set your color and size and press Ok. Mostly preferred 2pixile black border, it works for most sigs.

Oh, and I like your latest sigs they are getting better and better. But, try to include a little amount of pics, cause putting many might make the sig look crowded though in yours I don't see them crowded you do them very well. Well, Good Job on 'em all, keep at it. :up;