Il1 as in Eye, Elle, One, remain ambiguously similar in sans-serif fonts, and it’s 2015.
O0, as in Oh, Zero, also remains to be an issue, but most fonts make the distinction pretty clear.
I cross my sevens and have gotten into the habit of crossing zeros too.
But what about ones? What should I do? If I’m jotting down my router’s info on a piece of paper, when it comes to ones, I usually end up using my artistic skills to make a serif one, with a little mullet hairdo at the top and a green army man style base at the bottom.
And capital “I” (sounds like eye), I just give the the horizontal serifs on top and bottom.