Sun Sigil: To get this item, you have to win the Catcher Chocobo challenge with a total time of 0,0,0
Moon Sigil: Once you have gotten all aeons (including the Magus Sisters), go back to Remiem Temple (in the mountains east of the Calm Lands) and challenge Belgemine. Defeat all of the aeons and send Belgemine to win the Moon Sigil necessary to upgrade Yuna's legendary weapon.
Mars Sigil: Getting the Mars Sigil is a time consuming task. You need to unlock 10 Area Creations or Species Creations monsters at the Calm Lands Monster Arena. To do this, capture 10 different monsters in 10 different regions for the Area Creations or 10 monsters of each of the 10 species for Species Creations.
Jupiter Sigil: The Jupiter Sigil is a random prize you can win in the Blitzball league matches. However, it will only appear if Wakka has learned the Attack, Status, and Aurochs Reels
Venus Sigil: Dodge lightning 200 times in a row
Saturn Sigil: Once you've got the airship, return to Macalania Woods and compete in the butterfly challenge
Mercury Sigil: This is hidden in Sanubia Desert. Look for the rock with the Cactuar picture on it. Examine it to get info about 10 Cactuars that hide throughout the desert. Find each Cactuar and you will be able to play a game of Red Light Green Light against them. If you reach the Cactuar before the timer runs out you will be able to battle it. The prize for battling is a Cactuar sphere. If you happen to lose three times, you will get a Sphere del Perdedor. Whenever you get a new sphere, go back to the Cactuar rock and place the sphere into the stone. Perdedor spheres will work fine as well, but the more Cactuar spheres you get, the better the treasures you will get in the secret area that follows (get eight or nine Cactuar spheres and you will find a Friend Sphere, for example). After you have placed nine spheres in the rock, you will be able to get into Cactuar Village (which was previously obscured by a sandstorm). Inside, you will find the Mercury Sigil.
I've done the butterfly thingy but i still can't get the sigil!