Where are the clickable places?

Hint 1 of 7:

Try the edges of everything.

Hint 2 of 7:

The four holes in the ground abound with items.

Hint 3 of 7:

The top edge of the screen is good.

Hint 4 of 7:

Try the right screen edge, and the bottom.

Hint 5 of 7:

Try the left horizon line.

Hint 6 of 7:

Don't forget the bottom edge of the screen.

Hint 7 of 7:

And of course, the sign itself!