How to escape the (hash) # sign in a Github markdown header? (backslash is not working)
Solution 1:
You could try and add a matching '#', followed by one extra '#':
### C# #
Solution 2:
You can also use # in place of the # symbol (based on this meta answer).
Or, as in this answer you can insert an invisible character before the octothorp, such as ​.
Solution 3:
Add an extra space after ### C\#. See the demo.