Sigils and circles

[MississippiStarChildGambler]

Does anyone of you know what the sigil on the front of the Necronomicon actually is? Best info I can find is that it is known as "the sigil of the gateway". Is this true? Any info you guys have I would be very grateful for. Especially wanna know if this particular sigil shouldn't be encircled as well for reasons I can't give here without letting personal info out about myself.