one has two quote marks; the other only one colon.

But "less keystrokes" is a glib argument in favour of symbols... a
better reason for using symbols over strings is that symbols are more
efficient in memory. They act like pointers to a single string, where
quoted-strings all exist individually in memory, so if you use the
same string a lot, you use lots more memory than if you use the same
symbol a lot.

Michael Pavling wrote:

The difference is that a given symbol only exists in memory once
whereas you could have many copies of an identical string floating
around, each using however many bytes. The flipside is that symbols
are never released. See also