When in Markdown source an HTML comment contains Markdown's link markup, the resulting HTML contains link placeholder in place of the comment's text:
Example.md:
Please see <!-- [Example][1] -->
[1]: http://example.com/
Example.html (rendered with python-markdown 2.0.3):
<p>Please see <!-- �klzzwxh:0000� --></p>
Actually there are STX and EXT chars in the output, they are just not shown.