The independent web-publishing firm Exis has been engaging in a number of A/B tests measuring the success of the "list" (or sometimes called the hamburger) icon. Their last test was statistically significant to start drawing some conclusions. Some of their key findings:
- The word "Menu" performed about 20% than the "list icon."
- Android were 3x less likely to click a navigation button than iOS users.
The Nielsen Norman Group released an updated study in February 2014 on the success of icons today. While they found that most users understood the magnify glass to mean "Search", most users still do not understand newer icons such as the list/hamburger icon and map marker.
Labels should still be used for newer icons, such as the three-line menu icon (or “hamburger” icon). The map-marker icon is another icon with a still cloudy meaning and inconsistent use. Sometimes it means current location, or a different particular location, or locations in general, or nearby places. Users are still learning what these icons mean and how they behave, so it’s best to use a clear label.
So to answer your questions:
- No, enough users don't know that the list/hamburger icon means "Menu". Use a label if you want to use the icon.
- "But Medium doesn't use it!" True enough, but most people land on article pages. The team there is much more interested figuring out articles close to the one that interested you enough to click on a link then provide some bulky UI to find stuff yourself. This is why search is completely buried in the menu. It's just not important. If the team there wanted more people to use the menu more, they would call it out better. This is an intentional decision to focus the user on the article page and suggest more articles at the end.
- At this point, anyone would be hard-pressed to say that the "list/hamburger" icon is the international symbol for "Menu." It could achieve that status over time, but it'll be a while. In the meantime, providing clear labels with the icon helps users to learn the symbol.