What is the name of this type of riddle?

One of my former teachers used to have brain teasers on the board almost everyday. They were the type that had pictures and symbols and words written in a specific way so that you had to read them literally to get the meaning. I can’t think of an example beyond having a picture of an eye, then a heart and a U to mean “I love you” and so on.. Can anyone name these brain teasers?