WikimediaUI icon standard set in OOUI features a white question mark on black circle background [[ https://github.com/wikimedia/oojs-ui/blob/master/src/themes/wikimediaui/images/icons/helpOutlined-ltr.svg | labelled 'helpNotice' ]], for use in places like frameless icon-only buttons, #RevisionSlider as one example.
It also has a black on transparent '?' icon 'help' [[ https://github.com/wikimedia/oojs-ui/blob/master/src/themes/wikimediaui/images/icons/help-ltr.svg | help-ltr.svg ]] for use in toolbars, #VisualEditor's toolbar or #Echo's dropdown as examples.
Other, non-standard help icons in use:
[] MW core's `mediawiki.helplink` RL module for the "help indicator" on wiki pages uses a slightly different version of this icon in [[ https://phabricator.wikimedia.org/source/mediawiki/browse/master/resources/src/mediawiki.helplink/images/ | resources/src/mediawiki.helplink/images/ ]]
Active Extensions/Gadgets/web:
[] Echo's former icon is on commons as [[ https://commons.wikimedia.org/wiki/File:Echo_question.svg | File:Echo question.svg]] and is used by the [[ https://commons.wikimedia.org/wiki/Help:Gadget-ImageAnnotator | ImageAnnotator gadget ]]
[] Translate
/resources/images/help.png (c0c4771eee4a517536f5055bdcd4d433c08e19ce / [[https://wikimedia.mingle.thoughtworks.com/projects/language_engineering/cards/410|#410]]) and help.svg (014b5632fcc6a4200d519cf7f86e94c09639af8f)
[] UniversalLanguageSelector
{F26625036 width=20} UniversalLanguageSelector/resources/images/help.svg and help.png
[] VE's icon is on Commons as [[ https://commons.wikimedia.org/wiki/File:VisualEditor_-_Icon_-_Help.svg | File:VisualEditor_-_Icon_-_Help.svg]] and has some usage, particularly on frwiki.
- extensions/Collection/images/silk-help.png
- extensions/WebFonts/resources/images/help.png