1st sig - brighten up the ironman figures...renders? Too dark for the background imo. First thing I would do though is consider changing the text colours. Maybe, make the font bigger and do something fancy across one side of the background!?
2nd sig - Not too sure what you want to do with this one lol. You know what would be cool though!? If you could place a faded render/picture in some of those circle bubbles!? Create a themed anime/manga sig or something similar. The black background is bit plain looking atm but I guess once you get some more ideas for the sig that'll be easy to fix.
3rd sig - I like the idea. I would remove the grey background and focus on an airplane/airport theme tbh. There are so many cool plane wallpapers that you could use for it. It would look neat!
4th sig - looks about 80% complete to me. You just need to play around with the simple stuff like the text. I wouldn't change much on that one tbh.
5th sig - n/a
6th sig - AWESOME! Love it! No need to change or add anything! :333
Hai Coffee. Thought I would drop by and give ya a