And the answer is.......
Annex 14 to the International Convention on Civil Aviation says
Characteristics
7.1.4 The closed marking shall be of the form and proportions
as detailed in Figure 7-1, Illustration a), when displayed
on a runway, and shall be of the form and proportions as
detailed in Figure 7-1, Illustration b), when displayed on a
taxiway. The marking shall be white when displayed on a
runway and shall be yellow when displayed on a taxiway.
No doubt someone will explain what they do in the case of 08L/26R Gatwick which is a taxiway most of the time and a runway some of the time.
