◊—parallelism section symbol
For example, ◊6 is parallelism section 6, the section on parallelisms between Shakespeare and Sandys.
Ø—null symbol
The item is either not available, does not exist, or could not be located.
∞—search engine failure symbol
For example, Google's search engine may fail to detect certain words, or even entire lines, across all digital copies of some particular work. When such a failure occurs, if my goal is to highlight some text of interest, then I will usually try to highlight some nearby text instead.
Symbols