I Saw this in a movie and it made me think a lot about context which is a large part of what we do in graphic design. Read these two lines from left to right, first the top row then the second row.
You probably read both of these lines perfectly. What is interesting though is that the 13 and the B are the same mark. You only read 13 when there are numbers there and you only B when there are letters there.
This shows that context has a lot of power. It has the power to allow others to see different ideas with the same mark.