Manual:$wgVectorUseIconWatch/en

{{SettingSummary (1.16-1.21) }}
 * name = VectorUseIconWatch
 * version_min = 1.16.0
 * rev_introduced = 57030
 * section = Skins
 * range = (boolean)
 * default =  {1.22+) ({{Gerrit|56529}}; {{git|55f9ec174214fa142b17f1d998dec393fb60e6c0}})
 * summary = Watch and unwatch as a star icon rather than a link (for Vector skin only).

Details
Watch and unwatch as a star icon in the primary navigation (rather than a link inside the actions dropdown menu):
 * true = use a watch/unwatch icon button
 * false = use watch/unwatch text link