Relevant Products: Exclaimer Cloud Signatures for Office 365 | Exclaimer Cloud Signatures for G Suite
You are trying to set up a signature design, that requires different banners which randomly rotate. But, this feature doesn't seem to be included in the portal.
To set up rotating Banner Ads, you need to set up the signatures similar to the below example.
First in the list should be the Main Signature, followed by individual banner signatures with the image embedded, or hosted inside. Then the end signature will be the disclaimer (if you have one)
On all the signatures, apart from the Disclaimer Signature, you will need to set up the rules to Process the Next Signature. This setting will allow the banners to appear after the main signature and, before the disclaimer.
Then, a Date and Time Rule is required to be set on each of the banners, this will allow them to rotate for a period of time, depending on how long this has been set for.
Finally on the disclaimer, set up the server side rule and, leave the 'Do Not Process the Next Signature' setting as it is.