New road signs go through a careful process of design, trial and approval before they appear on roads. This does not guarantee that road users will know much about them, or if they do, will comply with the sign's intent. This problem is highly relevant to new cycling infrastructure, as it often employs relatively new road signage. The case study here concerns the use of the "sharrow", short for shared lane arrow, in new cycling infrastructure in Wellington, New Zealand. Naturalistic video data are used to closely examine the situated detail of social interaction between cyclists and drivers. The analysis shows some support for the effectiveness of the sharrow, but also emphasises that it cannot be considered in isolation. This will not surprise road designers, but the intricacy of coordination in the road space has to be seen to be believed. Such consideration of cycling and driving in its phenomenal detail is useful for any attempt to improve mobility on roads. [ABSTRACT FROM AUTHOR]