Don't upload them into your sig
Right click whatever sig you want to use, and copy the image location.
Paste that link into your sig.
Wrap the link in image tags - [IMG*] LINK GOES HERE [/*IMG] without the '*'s
- I have NO clue man, some standard ones I found on deviant art I think, it's been months since I made a new sig haha. All my photoshop work now is Photo editting.