ok i guess i dont know this because i am new to the whole final fantasy thing, but can any one tell me what a sigil is. i have no idea???? and people r talkin about it and i am confused
plezz can some one explain

along your journey, you will have collected "crest's" (sun, saturn, mars..etc) these "crest's" are part of the ingredients of obtaining the ultimate weapons for each character, the "sigils" are another ingredient, you need the corresponding sigil and crest in order to get the maximum potential out of the weapons. There are other ingredients you need, but you might already have these, celestial mirror, and a weapon for each character. These are found all over Spira.

yes crests can usually be found around. as for sigils you have to do a little work for.

for ex. butterfly minigame
chocobo race (get a time of 0000 seconds)
dodge 200 lightning bolts in the thunderplanes