As FRex said SFML is not an engine.
Personally, I think "engine" is a nebulous term and, depending on the developer and what it is they're making and how they're using libraries (like SFML), they might have different definitions of what an "engine" qualifies as.
But besides, we don't have to encourage the "SFML is an engine" idea. The gears, to me, say SFML is the cogs in your engine, the part that makes the rest of the engine work.
Anyway, as for alternatives (thanks for the album!) I kind of liked
this one, though I'd tweak it a bit (remove the icons, maybe remove the ellipse, and maybe change the M and L so everything is italicized forwards... and I guess I'd play around with various stylizations of the S (and I guess the other letters, but I like the F)).