In Markdown syntax, a # at the start of a line indicates a section heading. However, for Pagure, something like #345 is meant to be a link to issue #345.

If you type #345 at the start of a line in Pagure, it's treated as a section heading, like so:

#345

Not as a link to issue #345, as it is if you just type it in the middle of a line, like that. I think that someone typing a number sign followed by some digits at the start of a line in an issue tracker is much more likely to be referring to an issue or pull request than they are trying to write a header line, so we should assume it's the former, not the latter.