The icon for a 2-hour says 'SP' on it.
Well duh, but why does it say that? >_>
It's not even a universal thing either; not all "SPs" with a duration effect have a SP icon. One familiar example (for me, at least) is RDM's Chainspell; has an entirely unique icon for some reason.
On a related note, that [S] that is tacked on the zone names to denote their past versions? Everyone says that it stands for Shadowreign, but is there anything in the game that actually confirmed that?