Zeros and Fishnets

Today while I graded tests, I noticed one student crossed his zeros with a slash from about 1 o'clock to 7 o'clock.  In a mathmatics based test, where null set is always in the realm of possible answers, this does not seem like a very good habit. I assume the slash is in order to distinguish the zeros from the letter "o". Again on a math test, "o" is not likely a common answer. I pointed out this observation to the professor. 

A few problems later, my professor had the test and mentioned that there were a bunch of zeros on an answer he was grading. $15,000. You need to cross those zeros or else someone might think your answer is "isooo" all in caps. That is a common answer to many, many calculus problems.

Unrelatedly, I was walking on campus and noticed that people in shorts, sitting at park tables when the sun is high, creates an illusion that everyone sitting is wearing fishnet stockings. The tables are made of that material commonly found as playground equipment. It is hard plastic with small holes all over. It reminds me of small-link chain fences.