Paragraph marks

In Show,

¶ symbol marks the end of a Paragraph (Usually from pressing the Return / Enter key)

⏎ symbol marks a Line Feed (Usually from a Shift-Return)

On a long document (manuscript, thesis, etc.), pressing Return multiple times in order to adapt your text layout to the page is the last thing you want. i.e. if you want two empty lines before each section title, just adapt your Heading 2 paragraph style settings accordingly, and make sure that you assign the Heading 2 style to all of your section titles (more info here).

In this spirit, and because I'd tend to assume that you having searched for a tool like Show is a sign that you're aiming at proper formatting, I chose to use a slightly different symbol for empty paragraphs, which just shouldn't exist :

❡ End of an empty Paragraph