Double sharps also exist; these have the symbol and raise a note by two semitones, or a whole step. Less often there are half or three-quarter sharps.
The Circle of fifths tells you how many sharps are in a key signature.
In tuning, sharp can also mean "slightly higher in pitch". If the same note is played on two instruments, and one is slightly higher, it is too sharp compared to the other.
In Unicode, the sharp symbol (♯) is at code point U+266F. Its HTML entity is ♯. The double sharp symbol (𝄪) is at U+1D12A. Some fonts do not show these symbols.
- The AB guide to Music Theory, part I.