For the record, here is the policy on oversized signatures announced a few weeks ago on the Atlas board.
It's been three weeks since I solicited suggestions for size limits. Here is my proposal:
1. Signatures must fit within the screen of a tablet in landscape mode - I use an Ellipsis 10 so I'll use that to check signatures.
2. Based on that device, I find that the height must be less than a single image height of 640 at 72 dpi.
3. The width must not cause posting controls to go off screen without using the slide bar. Personally I think that should apply to posts as well since an overly wide image throws off the whole page of the thread.
4. An account warning will be given and a pm sent to the account when a modadmin has been made aware of an oversize signature.
5. Failure to reduce the signature within 24 hours may result in a muted account. This will block the account from posting more oversized signatures on threads.
6. If the signature is fixed on a muted account the owner of the account will have to contact the modadmin to unmute.
My desire is to begin using this by the end of the week. Please post any relevant questions or concerns.