I'm on a really slow connection, and when a heavy thread comes up, I don't want annoying animated .gifs in people's signatures load instead of what I'd like to be reading. That is all I'd like to say, and farewell for now.

Turning off either signatures or images are more likely to help you since what you asked for isn't likely to be made any time soon.

There's technically a limit of 80KB total for signature images, but it is not readily enforced because it's difficult to notice. If you notice a signature whose images have a total size of more then 80KB, you could ask the person to change it or you could notify an administrator.

If 80KB maximum per signature is still too much for you, Monolith's suggestion is the best action to take.

I suggest you turn images off too.