kinda confused on what you mean but.. here's the answer I think you're asking for? x_x
Right click the image and click on "Copy image location"
Go to photobucket.com or imageshack and paste that where it says "choose image from the web"
Then use Photobucket/imageshacks link to have it in your sig.
If the website saves the image for you permanently, then just 'Copy Image location" and go to your profile and paste that between (img) (/img), replacing ( with [