[edit] [s]

or

[edit | s]

It's as short as you can get while keeping the primacy of 'edit'.  Also, the letter 's' makes sense for either 'source' or 'section'.

No idea what basic usability/design conventions that breaks, but I imagine 2 small icons won't be much more intuitive than a letter with a tooltip.

Alternately, with Erik's idea:

[edit] [<>]

In any case, as a reader, and even just as an editor I think the distraction of the animation makes the clutter tradeoff worth making.

Cheers,