Actually, when they were first enforced, we were told that it was the total for BOTH images. So, you were allowed a maximum of 800 pixels across the screen, and 100 pixels high on the screen, with a max of 30Kb. So, if you have 2 banners, both can add up to no more than 100 pixels high, or 800 pixels across (if you have then one above the other, you could have them both at 800 wide, but a max of 100 total for height; whereas for two side by side, they can both have a height of 100 pixels, but the total for the width can be no more than 800). Going by this, which was the original rule that we were given by the mods, Dave's sig is in fact too high. Same as, in total, the file size is too big. On their own, they both come in within the COC, but added together they are way over.
Mind you, this is just what we were told when these rules were implemented after the forum crash...
Zec