RIP (Remove-it permanently) an add-on for Mozilla (Firefox) will work also, but I had to experiment a bit in order to make it remove all occurrences.
When right-clicking and choosing the image to RIP, the 'RIP Advanced' >> 'All similar items' from the fly-out menu seemed to do the trick.
I hope this helps.
edit:Actually, that seemed to remove all signatures, not just the one. Hmm.... Back to experimenting.
The
QuickImage add-on for Firefox can remove/block images images via a toggle button on the toolbar (three states: off, block third-party, block all). If 'block third-party' is chosen, it leaves board avatars as-is, but replaces third-party sig images (or any image, for that matter) with the text: 'image'. If the image is a hyperlink, it retains the hyperlink property but replaces it with text.
It also has a function to stop image animations, which is a nice feature/possible alternative.
"People take different roads seeking fulfillment and happiness. Just because they're not on your road doesn't mean they've gotten lost." - The Dalai Lama