[JayOtter]

It's in the editor view, beside the undo button, at the top-right.

It's not visible if no changes have been made (if the consensus is that's a bad idea I'm happy to change it).

[nkrisc]

If no changes have been made since the last save you could replace the save button with a message that states something to that effect.

[JayOtter]

That sounds about right. Might fade it out and have that as the tooltip.

[WickyNilliams]

Disabled button is preferable to hiding