I suppose given an assumption of who uses DDG it's okay to use the icon, but my core point is really that it's not as common as one may think.
In general, solely using an icon instead of text (or a combination of the two) is poor from a usability standpoint. Within a mobile context, I can understand the general push towards more compact treatments, but an icon with three lines does not intrinsically have any definitive meaning. While the icon may be aesthetically pleasing, I always felt there were some more effective alternatives.
There's been some recent discussion and data generated related to this icon (1,2), some of which can obviously be debated, but I think it's safe to say it's not as ubiquitous as you may think.
Overall, I don't think the hidden drawer pattern (and the associated menu icon) are appropriate for the site when it's being used on a desktop. But, it's OK given the contents of it and understandable when the site seems to have been designed mobile first and responsive. I do think more time should be given to the final 'desktop' state for a lot of responsive designs these days, though.
I like the arrowed version that DDG uses; I haven't seen that elsewhere (that I can recall) so far. I think the arrows encourage clicking on it to find out what is behind it, and most folks will probably not want or need to access the information behind it anyway. I prefer less text clutter personally. My personal favorite menu indicator is a small triangle in the corner of the screen (that you mouse over to get to the menu), but that is even easier to miss if you aren't expecting it (the triangle needs to be large for touch interfaces but if standardized could be set to be tiny or not graphically displaying for folks who know it is there and have a mouse).
Also, even if not perfect, I would love if sites that use infinite scroll would standardize on something to get to the stuff that is usually in small text at the bottom, and that icon seems as good as anything to me.
Firefox just changed to the three lines menu icon for the main menu so a bunch more people who haven't noticed it before will be forced to figure out what it means.
In general, solely using an icon instead of text (or a combination of the two) is poor from a usability standpoint. Within a mobile context, I can understand the general push towards more compact treatments, but an icon with three lines does not intrinsically have any definitive meaning. While the icon may be aesthetically pleasing, I always felt there were some more effective alternatives.
There's been some recent discussion and data generated related to this icon (1,2), some of which can obviously be debated, but I think it's safe to say it's not as ubiquitous as you may think.
Overall, I don't think the hidden drawer pattern (and the associated menu icon) are appropriate for the site when it's being used on a desktop. But, it's OK given the contents of it and understandable when the site seems to have been designed mobile first and responsive. I do think more time should be given to the final 'desktop' state for a lot of responsive designs these days, though.
[1] http://jxnblk.tumblr.com/post/82486816704/an-update-on-the-h... [2] http://exisweb.net/menu-eats-hamburger