FINAL ANSWER
"spareoom.net" forbids you to use their images FROM INSIDE THEIR SITE. You may have the images but you have to save them and find your own place to store them.
They set it up in a way that it would deny access to anything other than their own web pages whenever one of their graphics was being used.
The only way to use images from spareoom.net is to display them on one of spareoom's pages, right click and SAVE IMAGE AS in order to put it on your home computer. Then find a place...such as a photobucket account...to store it for use on the forum.
I have temporarily hosted the images on royalmagi.org, but that domain dies in mid december. If you haven't saved them by then I'm afraid you're out of luck. Sorry about the big mystery here...they should have politely provided you with a graphic that explains, "This image may not be directly hotlinked." Instead they left you thinking you must have mistyped your code. Nope, your sig code was perfectly done in every way.