Thank you for the question and for your thoughts.
Although the Guidance for Nemeth Code within UEB does not address this directly, it is practical and considerate to list number sign symbols on the Special Symbols Page. Please refer to the discussion in the Ask an Expert topic special symbols for horizontal number lines for more information about number line symbols on a Special Symbols Page, including an example document that shows number line symbols in a cell-5-headed portion of a Special Symbols Page.
As in all Nemeth-within-UEB transcriptions, your Transcriber's Notes Page must include a note explaining that mathematical content is transcribed according to Nemeth Code (Braille Formats, 2016, section 2.6.1c).
I hope that helps. Thank you again for your question. You are not the only one who has it I'm sure!