did you ever use something like that? Make pictures in sigs smaller?
Never heard of it and I also operated many boards (phpBB) (on my own hostingplans + domain)

If you don't want to see the large pictures you can use Firefox and Addblock, you can filter all images you don't want to see, so it's easy to hide large images.

Creating rules about image-size in signature isn't an option for a board like this with soooo many members or there must be someone who can write a (java/php)-script to automate the size-checking...

But I totally agree with the original subject, sometimes it's getting very annoying when you have to scroll down for a few secs just to see only 1 line of text, scroll down for a few secs and see the next line (of the next post) and it's going on and on and on... (that's why I use the addblocker =D)