number sign (#): also called "pound sign", "hash mark", "double-cross mark", or "crosshatch".

number sign (#) [1]: symbol used to indicate a word boundary. For example, #C indicates a word-initial consonant (C), that is, one which follows a word boundary, while C# indicates a word-final consonant. [Spanish: símbolo de número[1]]

number sign (#) [2]: a symbol which is used (relatively rarely) to indicate a morpheme boundary which is stronger than one indicated with a plus sign [2] (+). [Spanish: símbolo de número[2]]