What does "Requires Independent Campaign" mean?

Some signs on the Blip network require their own separate campaign in order to advertise on them. 

Some signs on the Blip network have unique requirements for their usage. For this reason, they may be marked with a label that says "Requires Independent Campaign,".

This label means that this particular sign must be the only sign selected in a campaign in order for the campaign to run. It cannot be part of a campaign that has multiple signs selected.