Offer "Sleep" (or "Power save") as the fourth option in the power down dialog from the system menu
It may be time to revisit the usability and discoverability of user-triggered system suspend for desktops. While it is generally expected that suspend-to-ram is what happens when you close the lid of a laptop, that metaphor doesn't work that well for desktop machines, since there is no such thing as closing the lid.
GNOME Shell lets you suspend from software if you press and hold the Alt key while the system menu is open, and even then it doesn't label the button, just shows a culturally-biased "II" (pause) button.
I don't know the rationale for making it harder than it needs to be to access that action. In my view, it would make more sense for this to be a proper action in the dialog that pops up when you hit the (more recognizable) power button in that menu. There's "Cancel", "Restart", "Shutdown". I don't see why there couldn't be "Sleep" (or "Power save") as a fourth action button in that dialog. It would be discoverable and explicit, unlike the current implementation. It would also be more accessible (i.e.: keyboard-navigatable, readable by screen readers) I suspect.
Maybe Endless have come to similar findings in their user studies and this is already being considered somewhere, I don't know (I might be forgetting something)