The sign "Distance specifications with verbal addition - zipper only at '...m'" indicates a specific distance before a merge or a point where vehicles must adjust their positions for a zipper merge. This sign typically directs drivers to be aware that they need to prepare for merging traffic ahead.

In terms of traffic rules, the "zipper merge" is a method where vehicles alternate as they merge, similar to a zipper. Drivers should be respectful and allow others to merge without blocking, following the guideline specified on the sign, usually given in meters. This helps ensure a smoother flow of traffic and minimizes the risk of congestion and accidents.

If you have any specific questions or if there's a particular aspect you would like me to explain further, feel free to ask!